1. upgrades:
If you can and want to buy FluxCrystals, its your chioice (i don't ) but the sooner the better:
first: +10 max energy so you can store more and use your buffs better (as much as you can buy)

Rdy for lvl 25
second: +25 xp gain per hour so you level up even when you sleep (as much as you can buy)
third: +1 energy gain per hour so you can hunt more(as much as you can buy)

2.skills:
first: 10 points (after 1st 5 in primary) at least put in Recover for mutants or Bandage for Soldiers or Patch for Cyborgs so you can heal yourself anywhere on the map
second: save your skill points for 25 level Core skill: Data Processor (Adept Lerner for FS players) so you gain more xp from creatures.

3.strategy:
first:hunt only at full stam you will be more efficient when using buffs.
second: put your evolution points in damage.

This is what i have found out so far to help. If you disagree plz post.

For the Purist I recommend getting the skill called Regain. It Heals 10 HP (+ 0.2% of your total HP per point) upon use. This skill requires 10 PSI.