For what it's worth:
If you're thinking about going Artifice or Synthweaving for your crafting skill, then go Archeology, Scavenging, and Bioanalysis to start.
Any other crafting skill go Slicing/Scavenging/Bioanalysis.
Here's my theory:
Gathering in the field costs NOTHING. The more you explore planets, the more free materials you are going to come across just lying around the battlefield. You can only aquire these goodies if you have the proper gathering skill. This combo covers most of your bases.
You end up with gobs of materials. Some will be related to the crafting skill you'll eventually select. Some of it won't be. You can sell that on the Galactic Trade Network for a tidy profit. You can also drop that gathering skill, and then pickup your crafting skill of choice.
To determine if you have enough material on-hand to level your crafting skill from 1 to 400, use this spreadsheet:
You may find you have some excess, or some material you don't need at all. Again, you can sell this on the GTN for profit.
In the end you'll end up with a mission skill, crafting skill, and a gathering skill that will become your bread and butter.
But while you're leveling up it MAY be better to play it cheap, collect materials for free and get credits for them until you have a better idea which crafting direction you wish to pursue.