For Alchemy, the base combines aren't too complicated. The level of the item determines what Level of material you use and how many. For instance, a Level 25 item will use 5x Level 3 materials (e.g., Iron). Level 10/20/30/etc. are oddities as they use 10x Level 1/2/3/etc. materials as opposed to 1x Level 2/3/4/etc. ones. Then there's trends you can follow for most of them (e.g., all the Sling ammos are Strong Chip of X + Strong Stone + Niello) or just some "common" sense (e.g., Metal weapons will probably be Iron, Clothes are Cloths, Leather is Hide, etc.).
That said, I haven't used Alchemy too much if only due to not getting the drops I need. I have a lot of Level 30-ish items but none are ones I'd use and then the 40-50+ stuff I do have (Diamond Knuckles why?!) that I'd use, I don't have the materials for :/ I guess I could try converting my way up but eh, I'll just rely on my Summoned Seraphim + Spells and just buy what I need for the time being.
Also, finished FMAT with 58 quests done (59 counting it, I guess). Double-checked all the schools so I hope I didn't miss anything.