Much depends on the game in question. Some are extremely detailed and some less so.
My own direct experience is limited (currently in a low-graphics freebie MMORPG called 'Nexusclash') but, based on what I have experienced there and observed elsewhere, these set-ups frequently have their own online forums and many players often organize into factions or alliances. Groups specifically established to help newbies with online advice or even direct aid can often be found in the better games.
Time-wise, unless you are really hardcore, probably not a huge chunk of personal time. NC is nice and simple, and runs on a 12 hour cycle (more or less) but logging in and running my characters seldom takes more than 15 minutes and often much less. Some faction activities might ask for members to be available online at certain times if possible, but this is rarely written in stone. Generally, as long as you are helping your faction rather than hindering it, things are fine.
Noting too, that, depending on the game, joining a faction may not necessarily be required - may be lots of "independants" out there as well. But, it can be helpful for new guys.
Best advice I can think of is find a freebie to start with, just to get your feet wet. I quite enjoy Nexusclash (
http://www.nexusclash.com/ ), it has mostly nice folks, a Wiki and forum, and a sizable community.
Another possibility is Shintolin (
http://www.shintolin.co.uk/ ), of which I hear nice things.
Neither of these are "Trek" games, of course, but can provide useful experience. There are others, a lot of which allow playing for free, but may have a system where you can pay up for additional benefits or enhancements.
... Oh yes, and if you want to quit, you quit as in just stop playing. "They" aren't gonna hunt you down for being a no-show.
Good luck.
The most basic advice of all for online RPGs is right here:
