#1 Crew skill trainers in various locations will sell you additional artifice recipies of your skill level is high enough. You can also obtain schemetics trough drops and containers.
#2 There is one on the fleet near the cantina I believe and there should also be one on both factions homeworlds. There may be more around but I havent looked.
#3 Just doing quests should get you a fair bit of credits, pvp warzones and space missions can help a little too. Once you hit level 50 the daily quests give a fair bit.
#4 You can find moddable variants of all kinds of armour. What you cannot get are moddable earpieces, implants, relics and offhand items such as shields.
#5 I think the amount of items are similar, usefulness of said items to you is more of a deciding factor.
#6 He can be equipped with standard droid parts bought from shops/trade network, you may also get pieces for him from missions. you should beware, he cannot equip weapons and is only good as a healbot.
#7 You cannot craft droids.
Anyone can feel free to correct me if i'm wrong on any point.