The chapter 1 outfit doesn't require a lot of collecting. Mostly a lot of money. In addition to the diagrams and crafting fees, you are going to need to buy Silver Ore and Studded Leather: Silver Ore is scarce, and the amount of Oil you need to craft Studded Leather is prohibitive.
I'm a firm believer in mastering one tree as soon as possible, so you start getting Adrenaline effects early. There's plenty of time to take second upgrades in important low-level skills like Position, Aard, and Alchemist later.
For an alchemist character, I take Alchemist, then Side Effect and Harvester. This gets me to Catalysis, Potions, and Oils. Then I climb the tree via Transmutation, Metathesis, Condensation, Mutant, and Amplification. When I get there, I craft a Yellow Meteorite sword.
You don't need Impregnation until you've accumulated a stash of nice mutagens. Then take two points in Impregnation and start using your mutagens. I favor Critical Effects, Enhancement, and Power; if you cast signs a lot, the Concentration and sometimes-rare Madness mutagens are especially good. I don't use Strength or Vitality mutagens much; on Dark mode, the most dangerous enemies will kill you quickly even if you have strongly boosted armor or Vitality.
I like to play Dark mode with powerful weapons, because it takes attrition combat out of the game. You can't make a tank of yourself and wade into melees; you have to use caution and tactics to protect yourself. And when you do get the advantage of an enemy, you can do unto him before he does you.