For leveling - always take three gathering professions. Pick one that will supply mats for a crew skill you will level up once you've hit 50 and sell the other mats in stacks that are competitive with prices on GTN. Lower level mats will almost always sell for very little, but grade 5+ mats sell for large amounts of credits.
Biochem is not a money making profession. Cybertech is the way to go. Mods and armoring gear modifications will always have a high demand.
You can make easy money with biochem with only implants. Make blues and purples in the range of L21 to L40 targeting rich people leveling alts. You will have to buy the L21 schems on the GTN or via drops but they sell like hotcakes. Less than 1-2k worth of mats sell all day for 10k+ purples even more.
The easiest way to make money is not to target L50's or close but to sell to people leveling alts in the the L20- L40 range. My entire empire is almost exclusively based on prototype implants from L21-L35, purple critical/power 9, 11 and 13 enhancements and later on purple L49 augments.
What I used to make-
Armstech: Some barrels(only occasionally) and L49 purple augments.
Armortech: L49 purple augments and orange sets made to order.
Synthweaving: L49 purple Augments and orange sets made to order.
Cybertech: L20-L40ish armor and mods, hard work though 4 classes, concentrate on will/strength first. High end purple spaceships parts though I imagine the new stuff on the cartel market completely destroyed this market. Some low-level earpieces.
Artiface: L21-L35ish enhancements easy money all day. Some crystals, mainly yellow and orange to differentiate myself.
Biochem: Implants, implants and more implants. Again concentrate on will and strength first.
