You don't. You just spend what you have and go get more. If you really want to bother, you can go back and do early level heroic missions. Most reward 3 planetary coms each, and you can blow through even the Heroic 4s through Balmorra pretty easily. Doing the whole circuit (Cscant->Taris->NS->Tat->Aldrn->BM) takes about an hour and a half, and you should net about 65 more PComs.
Another options is, if you haven't grouped yet, get the Intro to Group finder quest, and use the GF to start a KDY run. It takes about 15-20 minutes (depending on group) and will net you 35 coms.
That said. Don't.
Since you when ahead and got the 12xp. Drop everything and go Strait to Makeb. With the quests there, (since they also benefit from 12xp) you'll get to 55 in about an hour. You should have a quest thingy on your ship. Saresh will tell you about Makeb and send you there.
When you disembark, look for a tall terminal clicky. They're sort of like transport terminals, only taller. They grant the GSI buff. It bolsters you to 55 with ~160ish gear. And gives you a perma heal. Basically, you'll be able to tear through anything on Makeb. Be warned that it doesn't persist through log-out or leaving the planet. I think it does persist through death though. In any case, there's a buff term at ever bind point on the planet.
In any case, it makes Makeb super easy. And you'll be able to finish the quest really quickly. The buff isn't applied to comps, so just use Kira and let her hack away at whatever. And you'll hit 55 well before you complete the quest chain. You'll also get some fairly decent greens as quest rewards.
And level 53 greens are almost as good as the 50 purple mods. And blue 53 mods are better, and you can get some off the GTN for not too much.
Anyway, the point is do your best to patch together some gear as quickly and as efficiently as possible. to get ~25k health and maybe 17k for Doc.
Then you can move on to Oricon. The quest chain there gives you a full set of 156 gear. Note the quests there are a bit tough (one in particular), and to get the complete set of gear you have to finish a Heroic 2+. The heroic is soloable if you play it safe and take it slow. (Follow Dulfy's guide.)
*One thing is, they were talking about adding the GSI buff to Oricon fairly recently. I really haven't paid attention since, anyone I go there with has better gear than the buff provides--and of course I've been focusing on leveling the last several weeks. So just look around to see if it's there.
Once you have that, finish up Doc's stuff with whatever you can off GTN. And you should be good to go to do Blackhole/Section X pretty easily to get basic coms.
However, instead of buying the current Basic gear, you might just want to farm the coms till you reach the cap. 186s (The current BiS gear.) will be available for Basic coms as soon as 3.0 goes live. So buying anything with them now is kind of a waste.
And I wouldn't waste too much time farming them anyway. Instead start a new class and take advantage of 12xp.
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