To answer your question: Yes you can hit 400 easily on any crafting skill as long as you're at least level 10 (so that you can learn the skill and have one companion).
The lowest useful level for a crafting alt is around 15-16, which is high enough to get your ship, giving you a second companion, and the ability to deploy two companions at once. I have three alts at this level that I have used to gear up others while leveling, until I decide to level them up.
For a little more effort you can get an alt to 25, which lets you deploy three companions, and for most classes probably gets you through the class quest where you will have at least three to use. For someone who just wants to do crafting and nothing else, getting 11 or 12 alts to level 25 is probably the biggest bang for the /played time invested in terms of what you can do.
To get four companions out you need to hit 41, which starts to feel like a lot of work for only 33% more crafting bandwidth than you had at 25.
To max out on crafting potential for a single toon, you will have at least five companions and can deploy all five on any class by level 48; but at that point it's not much longer to just go ahead and ding 50.
Also, once you can deploy two or three companions, go ahead and max out the affection on at least that many of them to make the most of them. The cheapest and quickest way to do this is just buy the full legacy gift giving perk, and use green gifts from the fleet vendor. It's a little tedious, but you can hit 8,000 affection in about 15 minutes or so just feeding them stacks of the optimal type of Rank 1 and Rank 2 green gifts. Use Rank 1s until the affection gain drops to zero (because with the legacy perk you get more affection / credit out of them than Rank 2s even when they drop down to +25 each), then use the Rank 2s to 8,000. Then pick up a dozen or so blue Rank 5 gifts of the optimal type off of GTN to finish them off.
With only two companions it's a little slow learning patterns, but still doable. I tend to log on mornings and evenings during the week just to tend my crafting alts and grind out mods for whatever toon I am leveling, and then on the weekends I have two or four levels worth of gear ready in the mailbox for my leveling toon to put on as needed. Once you have all the basic blue patterns for armorings, mods, enhancements, ears, implants, and offhands, it is simple to keep alts fully geared every two levels. This means you need at least a cybertech, artificer, and biochem toon. Armstech would let you make barrels as well, and offhands for your toons and companions that use cunning, but I haven't bothered with it yet since you get a guaranteed 30+ comms from every planet when you always take comms instead of gear and don't have to blow any on mods. That's more than enough to get the barrels you need at the end of each planet, and you can always pick up a shotgun or shiv off the GTN to fill that hole.
When I roll a new toon, the first thing I do after the noob planet is run them through BT / Esseles to ding Social I, hit the capital world to grab an orange social set for the toon and companion, then slap on the legacy Sandpeople Bloodguard belt and bracers on the companion, and in most cases the Renowned belt and bracers from the legacy vendors. With the orange weapon you get from the noob planet for yourself, and another for the companion that you can buy for commendations from the specialty vendor in a few more BT / Esseles daily runs, you're set for leveling from 11-49. Since I have a synthweaver and armormech with almost all of the orange sets, I might swap out the hideous social gear for something nicer looking later on, but the butt ugly social will get you through 25 or so just fine.