Ok so, i've "stormed the HFS" about 5 or so times now, over the course of my many forts - it's my end of choice when FPS death becomes too much, although in a recent fort i chose instead to abandon in order to save my historical migrants... anyway.
Generally in my attempts, i have had anywhere from 10 to 20 melee, and 20-60 ranged. In my earlier attempts, the crossbowers were decently trained but that was about it. In one of my solid attempts i had 12 all legendary hammerdwarves (that took a while, i don't use danger rooms), and 50 crossbowdwarves. The hammerdwarves were in mostly candy armor, steel war hammers, with some steel gauntlets / high boots.
Most of my attempts have involved just one giant room, melee spread out at the front, ranged spread out at the back.
Anyway, they all end the same. Legendary training or not, even in full candy, melee die in a heartbeat. Marksdwarves are good but they have no chance once the melee are down.
The main issue seems to be 1) the demons have AoE damage - area of effect. they spray a cloud of fire / poison / kittens or whatever and since there's just so damn many of them, anyone in range is going to be decimated. And then of course 2) they are incredibly tough in most cases (some fire / steam demons can die a little easier), and their attacks are rediculously overpowered. Again, even in candy armor, a simple kick to the head is all it takes. Or leg, or arm, pretty much any attack that lands will break bone.
So you need lots of powerful melee - but the more you have, the easier they die to the area effect damage, so you have to spread them out. But even then, they have a habbit of all running into the one spot, so you can't put all your money into the melee. Markdwarves however have a hard time landing killing blows.
Anyway i'm starting to ramble. So that is my experience - i think the best i have done is to kill maybe 25 of the 50ish demons that seem to spawn, before all my soldiers lie dead on the floor. Of course, i've never used the kind of numbers you're talking about, so you may have better luck.
My 1 piece of advice would be to spread out the battle as much as possible.. at least, without overdoing it to the point of exploit
After all, if you can't meet the HFS in honorable combat... what's the point?!