- If you see a glider circling as they do, will they generally continue in that turn or do they often reverse direction?
They will generally continue in that turn. But... They may be varying the turn radius to properly determine where the best lift is to be found in the thermal, and to center on it.
- Again, if a glider is circling is it generally ascending in a thermal (typical rate of ascent?)
Normally, yes. It doesn't make sense to circle in an area of still or descending air.
- Do gliders generally ask for a radar service?
Gliders generally do not use the radio at all, IME. Even their circuits are completely non-radio. Apart from the fact that most gliders in most places (except where required by law) don't have transponders so a radar service would be useless.
What does happen in a lot of places is that the gliding site will give the local ATC provider a ring when they commence gliding, and when all gliders are back on the ground. That way ATC can at least warn you that there are gliders in the general area.
And what is useful to know is that gliders generally (note: generally - there are exceptions) will be flying up to the base of the cumulus clouds, but not above.
What I strongly recommend is that you visit a gliding club for a day. Phone ahead and/or show up early (in time for the briefing), explain that you're a power pilot and want to sample the atmosphere, see the procedures and so forth, and you'll find that you're able to participate in the activities for a full day, no strings attached. With a bit of luck you can make three launches that day but also experience what happens on the ground. And get to talk to a lot of experienced glider pilots who can answer all your questions.
Oh, and that full day of gliding will probably be much cheaper than an hour of power flying.
I'm a power pilot but I've done two midweek gliding courses (and the third will happen in a few weeks time
). Not only did I become a better pilot (I finally know what the footrests are for) but it also made me much more aware of glider behaviour: where they can be found, what their typical pattern of operation is, and so forth.