The thing that bothered me, though, was this; my military dwarves were all in separate squads and none of them were ever in the barracks I designated. I never saw them sparring even once.
That's part of the problem, then. Squads of melee dwarves should be pairs, at least; they often don't spar reliably if they're singles. Marksdwarves, on the other hand, should be singles, since they often don't use archery ranges reliably if they're in a group.
Also, make absolutely certain that they're all actually off-duty with the (m)ilitary screen's (v)iew squads option. They won't spar if they're on-duty (though won't go to their station or onto their patrol route if they're off-duty).
Is it best to make a small food stockpile in the barracks to take from your main food stockpile so they have some food and drink?
It usually doesn't matter in my experience, but it is an option. Supposedly, dwarves won't spar on top of buildings, however, so make sure the stockpile doesn't cover the whole barracks.
Is it wise to make fortifications for the wall between your barracks and your trade depot?
Well, doing this can let your sparring dwarves actually see unstealthed invaders coming through the depot, so it can make you need to manage them less. However, if there are unstealthed invaders approaching your depot, you can probably just put your soldiers on duty and station them in the depot, so... Meh.
Should I make sure i've got some Z levels above your main entrance? If so, how can you do that?
Totally unnecessary. Some people like to build a guard tower out of constructed walls and floors and have marksdwarves stand up there where they can shoot at attackers. I usually don't bother.
As a somewhat inexperienced player, is it smart to choose a region with magma?
Magma is very useful, and very dangerous. I greatly prefer regions with magma, myself, but then again I know how to get it to where I can use it safely. On the other hand, trying to get it to where you can use it is the best way to learn to do so safely, so let's just say yes. At the very least, you'll have Fun
As for the booze idea, I have hundreds of barrels full of ale, and I have such a productive food industry that having one kitchen set to making lavish meals on repeat and my 88 dwarves dwarves can't eat it all before it goes bad.
Well, it was just a guess. I don't know what your problem with workers was/is. Since your engravers could get to the surface, that probably means that everyone else could, too, and I'm assuming you had the mining labor on your legendary miners, so I have no more ideas just from what you've mentioned.
...Though if you have been, avoid using ramps in the future. Staircases are much harder to screw up the placing of.
I did the upright spears because I was looking up traps and it said upright spear traps never jam and so are the better choice.
That... That's
true, but also grossly misleading. Upright spear/spike traps don't jam, but they also don't trigger automatically. You need to link them to a lever or pressure plate and then have something actually activate that lever or pressure plate, so they're actually much, much worse than weapon traps, which just trigger when an enemy walks on them. However, due to the whole stuck-ins things, spears aren't exactly the best trap weapons, either.
I'd go back to that fortress but it was a siege, which was by the way the first attack of any kind I was ever dealing with. By main entrance I mean that, I have a secondary entrance that was almost dug out, even though I have 5 legendary miners who just never do anything even with massive stockpiles completely full of barrels of booze and prepared meals, and a bunch of work orders they could fill in seconds that they just don't seem to path to. I was halfway done with a proper moat and a massive, winding secondary entrance that I was preparing to build massive amounts of cage traps, stonefall traps and some other traps, along with a few corridors for a flooding trap, and floodgates hooked up to a lever, along with two sets of double doors so I can let a siege force in, then if they make it past the drowning trap I was setting up, I could simply forbid the doors that enter into the main hallway from the trapped one. I was also working on building a tower for some marksdwarves.
Well, it sounds like your biggest problem was labor deficiencies for whatever reason. You'll actually probably find all that to be massive overkill. Hell, with that many preperations, I could probably take on orcs without my dwarves even needing to actually see one.