Reverse curls are where you take an overhand grip on a barbell, holding it in front of you down by your legs (as if you just picked it up off of the floor), then curl it up in a biceps curl motion. You won't be able to go as heavy as you do for your "regular" or underhand grip, barbell curls. It works the head of the biceps at a little different angle, and also hits the forearms.
On extensions, yes. Standing, sitting on a bench/chair/ball, and extending the leg to bring the weight up, contracting the quads. My tacky little home bench has a tacky little leg attachment I use. I much prefer squats and lunges for quad work, but throw in some extensions for variety and to hit the lower quads/teardrop area more.
Right now, I've been trying to put on muscle, and I'm a hard gainer. So I do "steady state" cardio, 4 days a week. One week I'll do 20 minute sessions, the next week I'll do 30 minute sessions, then back to 20 the next week. As I get closer to my contest, I'll incorporate HIIT (yes, interval)to really peel away the fat. If I did that right now, I'd lose too much muscle in the process. On my 20 minute weeks, I usually use the nordic track. On my 30 minute weeks, I'll use a Cathe pre-mix, usually from Step Blast (just because that's my favorite). Once I start HIIT, I'll go back to IMAX 2 and Boot Camp, probably using pre-mixes, because I'll add it in increasing increments from 20 minutes one week, 30 the next, 35 the next, etc. I'll have to do it progressive like that to shock my body. It can become accustomed to cardio and weights and plateau, just like it does with the same food all the time.