I always advocate going against the dragons first for the sake of the BMU. We're experienced enough to do so:
Now I don't know what happened, but I could not hurt Draconis at the gate with the FoA. Fortunately the upped Foebane did the trick. Don't forget to hop away sleeping (recharging your ability-pool).
Inside the Lair there's the should-be-infamous ice salamander room. If you have a prot from cold scroll, I highly advise you casting it.
And if you have a bunch of potion of invisibility (or ring, or whatever), I advise to avoid contacting the eyes. They are more trouble than their worth.
When you aquire the Bronze Pantallettes I strongly advise to hop for the BMU, and sleep (bad design causes your character not to sleep for a week). For the actual fight against Abazigal first crawl around the edge to get rid of the salamanders (use ranged weapon - scorching BMR, wink, wink), and only when that's finished and you're regenerated start trying your luck against the dragon.
What I actually HATE in dragons their ability to just smash away 50% of your HP. Annoyingly dangerous. So cast a Hardiness WHILE you're still fighting his human form, than whirlwind it to oblivion (and reload if fail). The whole thing is just stupid, because he not just able to smash your HP for reasons, but you also not have time to drink potion 'cause it can fullheal for reasons. Still, with baba even this fight isn't too long or neigh impossible.
Trial 3 is the lamest of all.
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Sendai
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You may swap back the Human Flesh armor, as drows are ... civilized, thus will trust in spells, but Crom rejects that... I mean... You get it.
I say choose the slave-tunnel. As you have weapon immunity it'll count. But you'll also need a good AC, so as soon as you enter PAUSE the game, and
for this fight, and this fight only, swap the BMU. With Defender of Earthheaven you'll have -20 AC, so the Duero Berserkers, the only units able to hurt you, won't (constantly) hit you. This is semi-cheating as as soon as you enter you're "in battle", so if you're nosey, you might try going through in the white dragon scales. I on the other hand say the smallness of the doors is just bad design.
The Bowstring of Gond would be a useful item IF ranged weapons would not be obsolate in ToB (we'd go for the Talarash bow, but there's rly no place to use it). Oh, if you insist as the duel with the drow captain is a fighter battle you can play the same armorswapping as for th slave-tunnel, but he has not that many HP...
For Sendai itself... It is a prolonged fight, but I give you some rules:
#1 always kill those at the door. They are annoying, but do not respawn.
#2 sleep before this battle, lol
#3 you probably want to bring in all yur buffing equipment. Haste, improved haste, stone skin, mirror image - you name it, are useful.
#4 keep healing yourself
#5 if you don't move from the door you likely can enter non-battle mode as the statues don't notice you until they notice you
#6 your biggest weapon is the Pocket Plane ability. If you dig yourself into a hole, you can just hop away (might require non-battle mode!), sleep a good sleep, while Sendai is at your mercy :P
The biggest problem with Sendai comes with her last/real apparition: she can strip ALL your HP but 1, which is that ridiculous healer-spell. So I strongly advise to SAVE between stages when the ones coming through the door are disposed, but her new form is still out of screen!
Aside that with baba this fight is probably way easier than with any other classes.
Trial 4:
Cyric's backstabbers are no problem for someone immun to backstabbing. Still, if you have any enchantment left, or you slept, you can cast it.