Try doing the daily space quests (rather than just doing missions without quests), and also try doing the high level space missions. If you're only getting 300 creds from your space missions it sounds like you're doing the lowest level space missions. Harder the mission the higher the reward.
As for PvP, you can try using a focus build, so far it's proven to be the most viable PvP build for Guardians. The tanks build is ok but just lacking a bit in dmg output, vigilance is problematic due to survivability and lack of a decent CC. That being said, both the tank and vigilance builds aren't totally useless in PvP and can be quite effective against players not so accustomed to PvP.
As for crafting, being a Jedi (either JK or Consular), you cop the weakest companion synergies for crafting. That being said, JKs are quite good at biochem, and biochem pots are quite handy and sell nicely. Personally I ran down the cybertech tree as a JK, even though I got basically no companion synergies with it, and it's working out just fine, except that at later stages you miss the efficiency bonuses on mission times.
Money making wise, most people either craft heavily sought after equips or sell high demand resources.