As I've been leveling up my Commando, I have tried to keep my crew skills in pace. I have Armstech, Scavenging and Investigation all around 200 at the moment. So far, I have done pretty well selling what I craft, specifically Barrels ( Artifact/Purple ). I also use them for my character and my primary companion.
The big hurdle for me was how to get enough Artifact (or Purple) materials to craft Advanced modifications. Normal Investigation missions only have a small chance to give purple mats. It's much too expensive to rely on them to craft.
That's where Crew Missions come in. These are obtained through Slicing and often for sale on the GTN (AH). Once purchased, just right click on one in your inventory and the mission will be added to you Crew Skill window. It takes a bit longer than the average mission, but is worth the extra time.
If your companion is successful, they'll bring back a number of different goods. Most importantly, Artifact/Purple crafting materials like Polyfibe or Ceraglass. This is a very reliable way to be able to produce the best crafting items.