I had some (succesful) MP experience with Bogarus, so hope I can give some advise.
>> However bogarus has no real access to death, nature, and water.
They have death 1.

If you manage to get at least some death income, its enough to start magically searching with dark knowledge. Afterwards, its one empower - and you can forge a booster for a total of D3 mage. Then, there are rings of sorcery and wizardry, helm booster etc. I didnt bother with it, though, and just started forging skull mentors.
No nature magic hurts like hell - your army relies on numbers, so supplies are needed. Also, you cant really equip thugs without nature.

I took a Wyrm with W3E3 and dominion 10. He did a great job at expanding, then found some earth and water sites, and then he summoned Beregynia. These are W3N2E1 mages, able to forge clam rings, wine shields etc. One of the most useful summons at your disposal. Wyrm or not, I think Bogarus pretender should be able to summon Beregini, I doubt I could've won without them.
And E9 bless is (imho) unnecessary. Your mages arent sacred, and even if they were, rejuvenation spell removes all fatique from all communion slaves. The only bless I'd consider is Nature - your mages are SO old, they get diseased even with Growth 1 too damn often. Since you wont be crafting boots of youth soon, shrout of saint with a regenerating bless might let your most valuable Starets live even after he's been diseased. I had one with astral 4 - and God did I wish I had a Nature bless. Thankfully, I managed to trade for a Ring of regeneration for him.