Ok, I am going to attempt to answer all of your questions one at a time.
First of all, you wondered about clothing and arming your dwarves. While is does become a problem at some point, it doesn't usually for a while, you have at least enough time to buy cloth from the merchants (they always come with a ton) and build a couple workshops. Arms-wise, you should only have weapons in use by your military, and you shouldn't need a ton of military dwarves, it is always most efficient to have your defenses based around traps.
Secondly: bedrooms. I have found that it is best (until you reach the population cap, although that tends to be a bit buggy) to have all of your dwarves sleep in one giant dormitory with many beds. You can do this by building a bedroom that encompasses all of the beds in the area and then toggling "dormitory" to "Y." This way, you have one area where all of your dwarves sleep, and the only thing you will need to worry about is having enough beds. You probably only need the number of beds to be 25% of the number of dwarves you have, as that should cover all the sleeping dwarves. It is even better to have a much larger room with half of it being a statue garden, as then you will have dwarves in the room who are awake and will see it if any vampires start killing dwarves.
For pens and pastures, there isn't a great way to make them efficient that I have found. There isn't really a great need to have them, though, because you can buy a lot of cheese and cloth from merchants. The only reason you would need a pasture, I've found, is for a chicken egg-laying area, but for that, you can make it underground in stone, you just need to be sure to have nest-boxes.
Building configuration-wise, I find that it is good to have a set plan for design before-hand. For example, know that you will put a lot of your workshops in one area, and your meeting hall and bedroom (see above) in another. It's also good practice to only dig out enough room for the workshop and not to group them all together in one room. You should also have rooms for your stockpiles near the corresponding workshops. Also be sure to have one "main" hallway, it should be 3-wide or more, as this will prevent traffic jams down the road.
Finally: farms. I would recommend you build a couple plump-helmet farms, as large as possible, to feed your dwarves. Seeds shouldn't be a problem, just go to the overview (z) menu, move over to kitchen, and disable plump helmets for cooking but not for brewing. You should have several breweries to make alcohol, and these will also return seeds. It is also good to have an egg-laying center (see above) and a kitchen. Hens and roosters will produce a ton of eggs, and if you set your kitchen to auto-repeat cooking easy meals, you should be able to feed your dwarves.
Best Answer
Any dwarf not doing anything should haul. This lets you turn hauling off of your more specialized dwarves so that they can focus at their task at hand.
Masonry and carpentry construction is also a good choice for migrant workers. Turn these skills on for all your peons, then make sure to set all of your workshops to require some existing level of skill. This prevents your unskilled dwarves from crafting, but allows them to construct walls, floors, etc. It's great fun watching a building go up in seconds with 50 unskilled dwarves rushing around placing walls.
Masonry is also good for carving blocks from stone. This allows you to stack them in bins, clearing up your stone excavated from mining. Set up a few masons' shops and tell them to repeatedly craft stone blocks. You may want to set the required skill level to none through some low level of skill. This means your master masons will focus on other crafts, and acts as a training program for masons, as once they've reached the required skill level they'll let another less skilled dwarf take over.
Stone smoothing is another great occupation for migrant workers. Smoothing large areas of your fortress is a great way to build wealth and keep people happy. Since smooth stone (as opposed to engraved stone) has no quality level, it's perfect for unskilled labor. Just be careful - increasing wealth like this can be unsustainable, as it attracts more migrants which you may not be ready for if all of your wealth is just smoothed floors.
Mining is a good occupation for migrant dwarves as well. Unskilled miners produce less stone while digging, meaning less hauling jobs and less stone to store or destroy. Just be sure to keep them away from valuable stone and ores.
Lastly, make sure you keep training your militia. Having a strong army is essential to a fun Dwarf Fortress game. Yes you can wall yourself off completely but mastering the militia is one of the most challenging and rewarding parts of the game. There's way too much to go into here, but the wiki has an ≡article≡ on managing a military.