A few diffrent Qustions about weight lifting?

First question- eat more, get better quality sleep.

Second question- I see no reason for some one at your age to not train 5 days a week. Again, if you are eating enough and sleeping enough this is not an issue.

Third question- have no idea, curls are not really important.

Increase what?

I find light cardio helps. Gets the blood flowing to the muscles to promote healing. If I sit around too much after an intense workout I get stiff and sore. Keep moving if you can. Don't forget to get a good stretch in after your workouts. I used to always skip them and didn't think they did much but they absolutely do make a difference. I know it may sound "girly" but yoga is awesome on recovery days. I find it helps the healing process along.

You should rest the muscle group you worked at least 48 hours before working it again. If you're still sore, you need to wait longer. You can work a different muscle group every day if you want. I personally stick to 3 days a week lifting or else I eat like pig and eventually succumb to overtraining.

The general recommendation is 8-12 reps before increasing weight, particularly for isolation exercises. For compound and powerlifts I prefer to work in the 4-8 rep zone for strength increase.

For isolation, I'd say 3-5 lbs. As much as you can lift for your minimum rep requirement.