1. tighter fitting clothes might not be a bad thing if it is from changes in body composition favoring added lean body mass

2. measurements are fine about every two weeks. skin fold measurements can be done a little more often

3. your routine is fine for now and it will probably work better for you this way as opposed to working certain bodyparts during the three days. for you, keep your rest times minimal and run through the circuit an extra time or two on at least one of the three days. your reps, sets and percentage of max load are far more important than the exercises themselves and should be adjusted at least occasionally.

4. substitute some of your machine movements with barbell and/or dumbbell movements at the beginning or middle of your routine until you can get to where the majority of your circuit is done this way. it doesn't all have to happen at once, so do it at your own pace.

5. focus on the positive (better looking arms, thinner face, down 51.5 lbs.) to keep your motivation high

IMHO, i think you are going about this the right way.