2: If you'd asked me 4 years ago, I would have been able to bring up the relevant code. Flaming weapon damage, while triggered by script, is handled by code. I want to say it's something like 1d6, with some modifier for weapon enchantment...
7: The bear-hunting comment is a reference to his hitpoint threshold. As I recall some of the higher-level named baddies (As I recall the devs called them "grudge monsters") have multiple spawning triggers, one relating to danger level and another relating to ingame time and max HP. Bears, having huge amounts of HP, usually trigger this second part.
8: Mellis is also a very useful god. He fills empty bottles and cans in your inventory (up to 5 of each IIRC) with random food/drink -- which means even ommel substances are possible (if highly rare). Loricatus you mentioned; his hardening is limited to the iron material chain, and behaves similarly to a scroll of hardening, including drawing off your own INT. Cleptia is amazingly handy, granting haste and invisibility at the cost of only a prayer, and Seges makes food pretty much a non-concern for the rest of the game. On Valpurus and Mortifer, one Vapurian altar is guaranteed in Attnam, so you can make sacrifices there if you like. Otherwise you'll have to get lucky, or polymorph another god's altar. Also, Mortifer's gifts are probably more useful than Valpurus', since by itself a valpurium 2h sword isn't all that great. Not to mention that two Neerc se'Ulb can (with difficulty) be used simultaneously to great effect -- something that can't be said about two valpurium shields.