Since patch 1.9 there is no maximum level anymore.
If you have a skill at 100 you can make it "Legendary". This resets the skill to 15, gives all perk points invested in that specific tree back. Be warned: You lose all the benefits of having a higher skill level! The advantages of making skills legendary are:
- Difficulty increase, since the enemies don't have their skills reduced.
- You can continue to level up and earn extra skill perks.
It is possible to repeatedly make a skill legendary or to make multiple skills legendary, this allows you to (slowly) unlock all perk points.
Level 81 is the maximum level in Skyrim without making any skill Legendary
There is a linearly constant amount of "experience" required for each level. The formula is simply:
(level-1) * 25 + 100
Where level is your current level.
"Experience" in this case is earned strictly through skill ups. Leveling a skill to X will give you X experience towards your next level. For instance, to level from level 1 to level 2, you require 100 experience. This means you can either raise 5 skills to level 20, one skill to level 21 (assuming it starts at 15), or any other permutation thereof.
Also, and this is important:
There is no soft cap
_
Level 81 is just as (relatively) easy to reach as Level 11, it just requires more total experience.
Since all races have +10 to one skill and +5 to five skills, this means there is a total of 88,085 "experience" to earn, and this is constant across the ten races. Level 82 would require 89,100 total experience, and is currently unreachable.
Thus, when your character maxes all of their skills, they will be level 81.
Try the mods, Better Dialogue Controls and Better MessageBox Controls.
Better Dialogue Controls description:
In A Nutshell
Have you ever pressed the E (activate) key in a dialogue
and it selected something else than you expected? Then you may find
this mod useful. Think of it as a patch for the controls of the
dialogue interface.
This mod will be most useful for people who like to use both the
keyboard and mouse, it fixes issues where the mouse just flat out
prevents some keyboard controls from working as expected. If you
exclusively use the mouse to scroll and click through dialogues you
may not have run into some of these issues. Likewise if you do not
move the mouse at all after entering a dialogue. If you move the mouse
pointer after entering a dialogue, then you will run into the issues
below:
- A fairly common occurrence is when you leave the mouse pointer somewhere over the menu and you want to use the keyboard controls. If
you like to switch to the keyboard navigation now and then, you will
run into issues where the mouse pointer just flat out prevents you
from scrolling to the top or bottom of the list with the keyboard
controls.
- Another common occurrence is that as you enter the dialogue, you think the first item, next to the pointy bit, is the selected item.
However when you press E, you find that the 2nd or 3rd item has been
selected. This happens because the mouse pointer takes the focus away
from the default option. Often times, I had to move the mouse pointer
out of the way when entering the dialogues because of this.
Solution:
- The mouse focus now highlights items, but does not make them active. Thus the active item is always at the center of the list (next to the arrow/pointy bit). When you enter a dialogue, the mouse
pointer never takes the focus away from the default option.
- The keyboard controls lets you scroll all the way to the first or last item, no matter if the mouse pointer is hanging over the menu.
- Scrolling the list with the mousewheel, or up/down controls always maintains the center item as the active one.
- You can still click off center dialogue items with the mouse, the mouse just won’t affect the menu until you click.
- The mousewheel scrolling has a smoother transition. It happens because I changed the mousewheel scrolling to work exactly as if you
pressed the up/down controls. I didn’t plan to change the mouse wheel
scrolling appearance, but I thought it was nice so left it in.
From: http://skyrim.nexusmods.com/mods/27371/
Better MessageBox Controls description:
In A Nutshell
This mod lets you navigate the message boxes with the keyboard. Use Left/Right controls, and Activate to select options
(typically A,D and E but it should work if you remapped those controls
to other keys). Fixes the clickable area of buttons so they are easier
to click.
Detailed Changes
These are the changes made to the vanilla (original) Skyrim message boxes:
- Enabled the gamepad style controls, which lets you navigate between options with the Left/Right keys (usually WASD), and select an option
with the Activate key (usually E) and Return/Enter keys. Now you can
dismiss simple “Ok” message boxes by pressing a single key instead of
being forced to click a tiny text label.
- The TAB key cycles through "Exit" type buttons, where the label matches exactly "Return", "Exit", "Done", "Cancel", "Back" or "No".
This helps navigate custom menus from mods that have lots of options.
While SkyUI3/MCM will alleviate this, there are still many instances
where mods will continue to use message boxes (or mods that won’t
update to use MCM).
- With SKSE enabled pressing ESCAPE picks the first “exit” button and selects it. Thus you can quickly exit out of most dialogs that provide
an “exit” button. The recognized “exit” buttons are exactly as for the
TAB key (see above). You can quickly exit out of Yes/No dialogs, and
mod options. In multi level mod options usually the ESCAPE key will
take you to the parent set of options, because it picks “Return”,
“Back” or “Cancel”, etc. WITHOUT SKSE the ESCAPE key behaves exactly
as the TAB key (I’m sorry but it was not possible otherwise to
distinguish the keys as crazy as it sounds!).
- Fixed the width of the clickable area for the buttons to properly adapt to the entire length of the button label.
- Extended the clickable area also below the button labels, instead of only above. This makes them easier to pick with the mouse.
- Added a subtle highlight to the focused button.
From: http://skyrim.nexusmods.com/mods/28170/
Best Answer
Yes to all five of these questions.
The stats limit thing requires some clarification: some stats have a bound above which they give no benefit (like armor rating or spell resistance), some are bound by variable size used to store them (You can't have a million billion hitpoints, but you can have several hundred thousand).
Changing and adding NPCs is one of the least important aspects of modding, you can change or add locations, graphics, gameplay mechanics, et cetera.
All mods on Skyrim Nexus are free, and so are the mods in the Steam Workshop. I am not aware of any sites that require payment to download Skyrim mods; though there might be some scammers around trying to sell mods, the mods they'll try to sell will likely have come from a free source.