The graphics and simplicity don't bother me much. The stop-motion-esque models put me off at first, but they've kinda grown on me. They have their own weird charm. I'm definitely interested in doing an FE11 ironman, so if you have a difficulty you'd recommend, I'd definitely appreciate it.
Well, while I personally think the FE6 hitrates are mostly fine, there are patches which adjust the hit rates. A lot of them come with a bunch of other changes though. Maybe I'll make a "minimal changes" patch some day. From what other, smarter people have said, FE6 is a game of risk minimization- the more misses your strategy can absorb, the better it is. This is a lot different from Conquest or what I've heard of FE12, where there are extremely precise but reliable solutions.
Woah now, don't go assuming I'm good just because I like the game. I'm terrible at Fire Emblem, though I do have some tips that can get you to Chapter 7, at which point I usually just go cry in the corner.
Use Marcus liberally to set up kills, or even just to finish dangerous enemies. He can tank a decent number of enemies, and if you're really desperate, try and train his axe rank so he can use Halberd. Personally, I think it's better to put the halberd on someone else, since Marcus is a strong contributor without it.
Javelins and hand-axes are actually very bad in FE6, it's a lot more focused on range-locked player-phase combat. This makes myrmidons and snipers actually good (but archers are still bad).
Don't turtle. The ambush spawns are largely placed where they'll screw you over if you're going slow. The chapter 6 ambush spawns are actually near the boss throne, so if you're going to be taking time to open all the chests, maybe give that room some space. They don't spawn for that many turns.
Bors isn't terrible for choking early points, provided he doesn't face any fighters. He and Marcus can hold down a lot of Chapter 3.
In an ironman setting, it might actually be better to just let Trek and Zealot die. It's sad, because I like them, but Chapter 7 is usually the point where I fail the most spectacularly. I'll admit that it's a bit of a harsh bump in difficulty, although I think odd difficulty curves actually work well for ironmans.
Mages are indeed very accurate, one of your few accurate unit types. Even if you don't promote them all, apply magic liberally- Lugh is a lot better than Lilina anyway.
Do an FE12 PMU, I already have some ideas. FE12 sounds like a thrilling game, I should get around to that too. Thracia as well.