It's definitely fun, though a lot of work too, you'll want to over-condition your horse...as in, train more than you think you need to because it does take more out of them than you'll expect. It's a good idea to start out with someone to guide you because there's a lot to it. I pay between $50 and $100 usually for the rides that I've done. They ARE expensive, which is why most people train a TON but don't actually compete all that often.
I have never been alone on the trail in competition. Now, partly this is because I always have a "riding buddy" who I ask to be placed with in starting order. (yes you usually get to pick someone to start with, at least through ECTRA-the local org. For me) If you stay with that person you'll not be alone on the trail, I think if you go it alone they assign you someone to start with-but that person may or may not stay with you.
As far as friendliness....I have met a TON of wonderful, friendly, helpful people through competitive trail--and most people who do this tend to be that way. You will of course get your snobby rich crowd as well who won't want anything to do with you...and you'll get some crabby poor-sports, it's just like any other discipline that way....but MOST people are great in my experience.
As for conditioning, do lots of longer walk/trot distances, hill training(walk them rather than trotting/cantering, that actually builds more muscle), some speed work, ride in groups to make sure that others passing or riding nearby won't be a bother. Practice things like dropping a sponge off the saddle into a bucket, taking pulse with a stethoscope, trying to count respiration(P+Rs), opening her mouth to look in at her gums, all things she'll have to allow being done to her at a CTR. I recommend a watch or gadget for training that will tell you your pace, distance, and total time at the least. Overall a CTR is going to be around a 5/6 mph pace. You don't have to go that speed the whole time, walk breaks are good, but you do have to average around there overall to complete it within your time frame. When you get closer to competition time there will be a lot to learn about what to do at a CTR...I won't go into that yet though.
See, I was in a more typing mood today! Haha let me know if you are wondering anything else...there are so many tricks to the trade, It's impossible to name them all at once.
A horse is the projection of peoples' views about themselves--strong, powerful, beautiful--and it has the capability of giving us escape from our mundane existance.