Another thing about your Comiisions Bridge Officers are that you will gain 2 new Commision Slots every time you gain a new rank all the way up to Rear/Admiral Lower Half. That means ultimately, you'll have 10 possible Commiissioned Officers. You'll be able to have specialize BOffs for certain circumstances. For example, I have a set of Bridge Officers I use when I'm going to be fight Borg on the ground or in Space. Another example, if you that you may not ordintally take Polarize Hull as a normal BOff ability. But you'll may want Polarize Hull when you go up again the Breen in space. They LOVE to use Tractor Beams.
Ultimately you my have a special set of Officers you use for your Away Teams, and the rest are used solely in space, or a mixture of both. It's one of the nice things about STO, you can buld your crew the way you want to .
I just want add this to what everyone else has said.
Don't worry that you need to get gear off of the exchange. You can get badges for exploration missions that can be used to get gear that is pretty good. And if you want to, PvP will give badges for gear along with EC. (but PvP can be slow at low levels) And there are a lot of mission rewards that are good also.
The nice thing about this game is it is not that gear centric. It is more skill based. You can even be pretty competitive in PvP without buying too much off of the exchange.
The game is forgiving in terms of having lower Mks of gear to a certain extent. But when you start hitting some extreme situations or certain foes (even with the Ground Combat problems), you'll want to have the best gear you can get. I specifically have Klingons in mind on the ground.
And at the rank Grades 8-10, the difficulty of enemies in space get's to be appreciable if you are still using lower Mk gear. You'll want to some better Mk gear (Shields and some of your weapons) to cut down on the difficulty a bit. I'm not saying enemies will be overwhelming but enemies will definitely be a bit more difficult than what you would be used to.
You get more if you sell them to a vendor than you do if you just recycle them with your replicator. When you recycle using your ship's replicator, I think you only get about 20% of the value of the item (as listed in the tooltip). If you sell to a vendor, you get 50% of the value.
This is really negligible when it comes to things like food, batteries, hypos. It is really noticeable when it comes to things like ship engines, deflectors, and other components. Selling to a vendor can get you an extra 10-20k for certain items that are very valuable. All those little increases save up over time.
Typically, I recycle all the "junk" I pick up, and try to save the bigger ticket items to sell to a vendor after the mission.