Personally, I find the easiest way to get started while doing other things (inviting the clowns to meet the first dwarven caravan is always fun, especially on a map with a shallow multi-level aquifer. Busy, busy, busy, but it's a small cost to keep out the riff-raff).
Where was I? Right, getting started is making a basic hospital, and setting up everyone as marksdorfs, all in case of early trouble. One butchered yak and some fishing gets everyone crossbows, bolts, and a helmet (maybe even leggings and gauntlets). Try to keep any cow if you get one for a while. The hospital gets a nice 7x7 room with 7 beds and 7 tables, which also have chairs so people can eat there, for now. It's also the dormitory, and your barracks, so dorfs do some dodge training rather than making friends, and they get a bed for their first sleep. Everything else is workshops and stockpiles.
Your 3x13 corridors are stockpiles. Your connecting rooms are workshops that use those piles and a couple 3x5 farms that will feed half the planet, remember after they plant the helmets you can switch the field to something else and they'll plant that in any remaining space, and so on. If you have stone immediately, that's awesome, get making the thousands of blocks you'll need, if not you cut down every tree on the map (or do that anyway, for bins).
Don't build a refuse stockpile for a while, try to use everything instead, it's a good habit. By the time the dorf caravan arrives you should be well safe on food, booze, building materials, and well into whatever megaproject looks fun on your particular map. Flat surfaces are good for covering in magma-pits, for instance, especially if you've modded body components so they all burn. Mountains with high cisterns (and what mountain doesn't end up with a high cistern) make wonderful deluges to greet the sieges with.
No, I'm not that good, but I have a lot of FUN trying, and the hospital/barracks/dormatory/office with minimal hauling distances for everything solves a lot of early problems.