I hope you will enjoy your mage, and I will try and answer your questions.
1. As far as I know it still holds true on p99 that if you give your pet armor, its AC will improve. I have heared that only the items that would show will affect it, but I dont know it that is true or not.
2. I dont recall it, and the mana calculator on old Castersrealm isnt working anymore, so I cant answer this question.
3. Mage pets start dual wielding at lvl 24 if you give it two 1h weapons and the highest lvl 39 pet dual wields without weapons. (Thats the fire pet that has a 35 DS)
4. I have been using
http://www.watson.org/~wander/eq/recipies.html for research recipes.
Hope this answers most of your questions. Enjoy P99!
Taeldar [50 Cleric] <Darkwind>
Crackling [40 Magician] <Darkwind>