The cost of fuel is in credits... like the ones you pick up randomly from enemies you kill and from selling trash items. So if it costs you 20 credits to travel somewhere it's coming directly out of your wallet and that's it.
Getting crafting experiences comes from sending crew on missions, gathering materials in the field and by actually crafting items. But you don't really need to worry about that right away, that's best left till you reach lv50 since working on your crafting early can burn through your credits pretty quickly. Best to save your credits for other things like buying your speeder license and speeder at lv25, lv40 and lv50.
Finally be careful of how many missions you have listed. The cap is 25 so if you reach it you'll have to end up abandoning flashpoint missions. That said, you can abandon flashpoints at any time and pick them up later, they'll always be playable.