First of all, welcome! Dwarf Fortress is a game with a huge learning curve, but once you really start to get your feet wet, the hassle of getting over the first few - or hundred - hurdles is completely worth it. When I first started learning this game, I had a lot of false starts. I even put the game down for over a year because the ASCII frustrated me to no end. I could puzzle out the commands and get started but even to this day, years later, the ASCII still gives me trouble.
I know most everyone here is suggesting you learn it anyway, but it can be something you do later, honestly. I just could not enjoy the game until I finally installed a graphics pack. I use Phoebus' set from the lazy newb pack. It's my favorite, but there are a lot of other good ones, so I would suggest looking around if you want to go with a graphics pack for learning the game.
The important thing is to take things in small doses, or chunks, and learning the ASCII symbols would definitely need to be a chunk all of its own when you decide to tackle it. One thing that helped me, is to start a fort with a graphics pack, get it going, and then switch back to the default. This way you have an idea of where everything is and you can 'k' look over everything to see what the different symbols are.
As for your other questions, while migration is the main way of building the fort population, you can build it more organically as well. It's just harder to do currently with all the changes to breeding and emotions. If you go with a starter pack, all of them should have a way to set both your pop cap, and you strict pop cap. The first one is used to mainly control how many dwarves are moving into your fort. Set this lower. I typically set mine at 20 for a brand new fort and then increase it as I need more dwarves. If you set the strict pop cap higher than the first, then births are allowed up to that number. I plan on doing a bit of a noah's ark fort where only the original seven and the harded coded first two waves are allowed into the fort. Every other citizen will be born there.
There are several different world sizes, and once you go to embark, you can set the size of your embark location from a measly 1x1, up to a pretty big size. Not sure what the max is, as my computer doesn't like anything over 4x4. You can also do embarks like 1x4, 2x3, etc. I'd do a couple of false starts to get an idea of how big each embark size is. It's one thing to give the tile numbers, but it's another to actually be in game and panning around to get a feel for just how big or small it's going to be. Default 3x3 is good for learning, however. Just remember smaller worlds and smaller embarks are typically kinder on your FPS. I'd suggest playing around with it and seeing how your computer handles larger worlds after getting your feet wet with the game.
Finding a good LP really depends. As someone else suggested though, I'd find a tutorial on YT, instead of a LP. I tried finding one when I was learning but there was something that usually made it unbearable for me. Either they couldn't speak clearly, they rushed and skipped over things, or I couldn't understand them because of an accent. There's a lot more stuff to be found now, but be aware of what version they're playing for the video. Most of the popular videos are for 34.11, and there are some big changes from those versions to current. Not big enough that they're useless, but enough that things might not work quite how you expect and it can be frustrating if the video says one thing and then it doesn't work for you.
As for advice, I will re-stress taking small steps. As others have said, set goals for each fort. Start small. Bring lots of food and booze if you don't want to worry about it right off the bat. Ditch the anvil and use the extra points for fish or booze or both. You won't need the anvil until you want to mess around with making weapons and armor. If you use a starter pack, you could even turn off invasions for your first fort or the first few until you want to learn how to fight. I use the Lazy Newb Pack. Most of them are pretty similar, but they all deserve a look. Aquifiers are hard at first. I'd suggest turning them off for your first games. Do what Thisfox did later. Start a world just for learning how to punch through them. Water in general can be dangerous, so be prepared for a lot of losses to drowning and pressure causing flooding.
And my biggest piece of advice? Don't be afraid to ask questions once you start. No matter obvious the answer may be to us, we're a good bunch that like helping each other out and having fun. That and be patient. If you get too frustrated with something, take a break, hit up the forums to ask why it's not working. Try again the next day. You're going to lose a lot of forts, but each one you learn and then suddenly you've been pulled in and things start clicking and suddenly the whole game just opens up.
Totally worth the learning curve and the time it took to surmount it for me. The complexities give this game so much life. It's been one of my staples for a long, long time. I may put it down for long stretches of time, but I always come back to it. Definitely a game to withstand time. It doesn't pretend to be anything but what it is.
Have fun dwarfing it up and experimenting!
Edit: Spelling, and whoops word wall.