Buying level 2 of Alchemy doesn't stop the potions from blowing up, they just do it less often. I think everyone has their own preference in buying tech, and I'm not sure what the best order is, but I don't bother with Leadership until I have done a lot of the others.

This is the order I usually use: science, restoration, medicine, alchemy, magic, leadership (only if I want a Chief this early otherwise I skip and do him after magic2), magic2, restoration3, medicine3, science3, leadership3, alchemy3, magic3

? I use cactus, cactus, lotus as the healing potion, I think it works more effectively.