Some good general info can be found at www.frets.com. Go to the index page and read the articles under the "Instrument Setup" heading.

I think it would be unwise to simply request a truss rod adjustment. It may or may not need that, and it may or may not need other adjustments or repairs. Go to a competent luthier and tell him the symptoms you're observing and the results you'd like to achieve. Rely on his expertise to advise you as to what needs to be done.

You should find answers to your specific questions at the frets website and/or from the luthier you deal with. Here, however, are some quick answers as I understand them:

Should I request anything more than an adjustment of the truss rod?...What other adjustments are made in setting up a guitar for maximum playability?
Yes, as mentioned above. Even if it only needs adjustment (and not, say, a neck set), it is usually necessary to deal with all three of the adjustments that comprise a setup. These are relief, the proper amount of neck bow, which is controlled by the truss rod; nut slot height, the proper height of the strings coming out of the nut, controlled by the depth of the grooves in the nut; and action, the the height of the strings off the fretboard, controlled by the saddle. It is necessary to adjust relief first, as it affects the other two. The action, and to a lesser extent the relief, need to be matched to your particular needs and playing style. If the frets themselves are significantly worn, that will have to be addressed in order to get good results from the adjustments.

Also, are there any differences between 12-string and 6-string setup procedures?
As far as I know, the procedures are essentially the same. It is important to be mindful of the different stresses involved with a 12-string, and in some cases make accomodations for them.