hey, you'll be fine and back playing tennis eventually. I've had 3 knee surgeries (torn ACL and meniscus, torn ACL, and scope to clean out scar tissue) and I just turned 23. The doctor will know if it's a torn meniscus when he's in there doing the surgery and will repair it if necessary.
First of all, DO ALL THE PHYSICAL THERAPY, but DON'T OVERDO IT EITHER. Just do exactly what your physical therapist says to do. Focus on getting the swelling down and keep your knee raised above your heart whenever you can in the beginning. I'd invest in some good gel ice packs or something similar. They seem to work a lot better than a ziploc bag with ice cubes. I'd also recommend spending some $$ on equipment to replicate what you do at PT at home once your physical therapist gives you things to do at home.
You should expect to be playing tennis (taking it easy though) in 6 to 8 months. That might be a little longer if you also tore the meniscus. No way to tell when you'll be back to 100%. It was very different for my two ACL surgeries.
looking through thread and will answer some of your other questions here.....
comfortable standing for several hours...to be honest, my knees get stiff after 30 minutes of standing in one place and I'm fully recovered. As long as I'm moving around, it's fine though.
100 degrees at 10 days post op is pretty good if I remember correctly. Just keep working on it and do what you can. That mainly has to do with how much swelling there is so it will improve with time as well.
You can always call your doctor's office and ask your doctor or a nurse questions. Your physical therapist will be a good resource too.
It's very possible to make a 100% recovery...I'd say I've easily made a 120% recovery. Depends on what you're expecting though....my knees pop a lot now and I don't quite have full range of motion on one knee, but it's pretty close. I had a lot of knee problems from playing tennis after surgery that I never had before. I now have a strict workout regiment...strength training, balance, agility...that I do 2 to 3 times a week and that has solved pretty much all my injury problems. I believe Andy Roddick had a torn ACL when he was younger and he's doing pretty well now I'd say
Good luck