So first, a couple of things I would do if you plan on doing something like this from scratch again in the future...
The first point I want to make is something I've learned from hard, bitter experience. Some players are incapable of separating inter-PC and inter-player conflict. It doesn't matter what their ages, experience or life skills are. This means you have to take this into account when you are planning on running a story that you anticipate will involve significant inter-PC conflict.
Also, where I am planning to run this kind of game, I always talk it over with players first. A little inter-PC conflict here and there is par for the course, but if I want it to play a bigger part then this conversation is essential. Some players simply don't like this style of play, or know that they find it difficult. Bringing it up at the start allows them to either back out gracefully or discuss possible compromises with you and the group. You can also get a lot of information about how your idea is going to work out simply by watching and listening to the way individual players react during this conversation. By the end of it you should have a good idea of whether your planned campaign is workable with this group of players, whether its a definite no-go, or whether you will need to make changes.
Now to cover your specific situation...
With this group, the first thing you need to do at the start of your next session is sit them down and outline your expectations. Players MUST be able to keep inter-character conflict in character. It is essential for the game to run smoothly for everyone's enjoyment. Don't try to lay any blame or point fingers here, just keep the discussion general and get all players agreement.
During play itself, if you or another player sense things are getting out of hand, then call a time-out. In character play immediately stops, no matter what the situation. Check whether there actually is a problem, as you might be misreading what is going on (something I've done on a number of occasions). If you still think there is an issue, take a break, allow people to get drinks etc, and talk individually to the players involved. Ask them why they were getting angry, what the problem was, and why they couldn't keep the conflict in character. Remind them of the agreement you made about this kind of thing, and if necessary bring those involved together to resolve anything outstanding away from the main group.
Assuming you've talked to the players directly involved and are happy with the responses, reconvene and carry on playing. However, this kind of thing may not resolve if players just find it hard to do this kind of roleplay without it seeping into inter-player conflict. If it happens regularly, then it will completely ruin the atmosphere in the group and rapidly lead to the breakdown of the campaign.
As a final note, given you've highlighted that a number of the players don't get on all that well out of game anyway, it's going to be a real challenge for you to keep any ill feeling from that coming into the game. It simply may not be possible depending on the players involved.
Yes, you can do that. I've done it.
It's a lot of work.
I used it to teach a group of kids how to play. As we went along, I introduced more and more rules to them to take the workload off.
The most difficult challenge in the beginning is to get the kids to know just what the character can do. You should start out with one or two key abilities and then add more abilities as they get use to them. Fighters are pretty easy at the beginning and their complexity ramps up nicely with learning. Sorcerers (as in your example) are almost as easy. The advanced classes that have lots of options are probably not well suited for beginners unless you want to do a lot of work. Even Clerics can be a bit of a pain with their ability to memorize most cleric spells in the book. I generally have the deity grant the ones that will likely be useful that day until they are up for the challenge of wading through the spell lists.
Give them a simplified character sheet that has stats, skills they can use, a combat section with weapons, maneuvers they can take and spells they can cast. I also add notes for stats and skills (high, mid, low) so they have an idea of how likely they are to be successful.
Then have a small listing of combat options: move + action, double move, and full attack. I give a brief description for each.
I then give them the dice they will need, telling them to roll the d20 for most things. As they learn what dice to roll for each thing, I have them write on the character sheet what die/dice the various actions use. This helps them learn.
Best Answer
Well. There is much advice and hints and tips and tricks to be learned. But I will keep on task, and I will help you in your specific situation. You can ask more questions later, relating to any other aspect of running a game that you want.
The Journey
The start of the ambush begins as the players first start on their way. You describe their surroundings, what kind of path, or road they are traveling, you ask them to describe how they are traveling, what things they bring with them, etc... because obviously as the GM you should know what your players are up to, how they are dressed, how they prepare themselves, etc. This lets the players describe to you their preparedness without them knowing they are doing that in preparation for an ambush.
Example: The players are just packing up their camp on their second morning on the road between two towns. You describe the path to them as muddy from the nights rains, and the scattered trees as glistening with rain drops, the breeze is sharp and slightly cold, and the sun is still rising over the horizon, You ask them to describe how they dress, how they prepare, because after all - the journey awaits. The warrior describes to you how he is wearing his armor and cape, but that he puts his bow in the wagon because he fears it getting dirty on the mud if he walks with it, and the wizard explains how since his robes are now soaking wet, he switches to his traveling gear (which incidentally, don't have his secret pocket full of alchemist fire flasks). etc etc.....
Misdirection
Here is an important part of the ambush, you want to check if maybe your players characters can detect the ambush, but you must do it in a way that they do not feel they are about to walk into an ambush. You want them to roll their perception (spot, listen, smelling, 6th sense - whatever) without knowing its for an ambush, and also after the roll, they should be feeling safe and unsuspecting.
Example: You describe to the players how they spot the carcass of a dead deer on the path ahead, and ask them to roll their perception. You generously describe the deer and its surroundings to those with higher rolls, and mention that it poses no threat since they can clearly see the animal was killed by a hunter who took its antlers. The players who may have initially been concerned with a dead body, are now calm and unafraid. And you have their perception rolls for the scene.
The Twitch
Something is not quite right. Some of the players may start to be suspicious, this indicates that the players have caught on to the fact that something may be afoot. Preferably this happens after you have already got everything in place, if not - you need to act fast before the ambush is too expected. Regardless, this is the point that you will be at right before The Reveal.
Example: A player may ask you "Will anything interesting happen here? Why are you describing to us this boring forest as we walk by?" Or "Dude, this is totally an ambush!" (okay, I don't have amazing examples)
The Reveal
This is the moment you have been building towards, it needs to be grand and really make your players feel surprised. Regardless, once the ambush is revealed, your deception is pretty much over, and combat (or fleeing) will begin.
Example: Maybe an arrow suddenly flies past them, narrowly missing them, signifying the start of the ambush. Or perhaps the shouts and screams of a dozen Kobolds suddenly surround them from all sides as they charge forth from the forests concealment.
On The Table
About what you do physically: Only pull out the map after the ambush has been revealed. Until then this is just a normal day traveling the road, and you describing the wonderful scenery. Based on their perception rolls and how they describe their characters, you will judge their preparedness (including their initiative rolls) to see if they can draw weapons, or prepare anything else for the ambush.