To answer your questions:
1. Strength and lean mass gains depend on the type of program, your diet and your body. If you're already 300 lbs of muscle at 5% bodyfat, CF *WILL* make you lose muscle mass. Basically, it's going to put you to near your optimal weight for your bodytype. If you're an average person like 180 lbs at 15-25% BF, it will probably add muscle and lean you down into the single digits for BF assuming you have a great diet, which, by the way, is the MOST important factor in gaining muscle mass.
2. Again, losing or gaining mass depends on how advanced you are beforehand. If you're squatting over 1000 lbs, chances are you're gonna lose some strength. Most people here with some direct strength work squat and DL above 400 with CF combined with max effort. If you're not there yet, this might be a good place to start (or at least Starting Strength program by Mark Rippetoe).
3. As I stated in another thread, if you're asking a question about full body vs. split routines, you probably (99% of the time) should be on a full body. I believe either Chad Waterbury or Charles Poliquin said it best about 80-90% of the people need to be on full body. If you're within 10% of your goal, split routines might be the answer, but if you're looking to add significant lean mass and drop BF, full body gives you MUCH more bang for your buck. (Also the reason why why compounds are better than isolation exercises in these cases)
The reason being that full body routines hit the muscles at least 3 if not more times a week on a m,w,f or greater schedule. On a split you're really only hitting your muscles once a week which is not optimal for muscle growth or strength.
4. Push/pull is better than upper/lower as you can hit a push/pull muscles more times a week than an upper/lower. Plus, it relatively evens out muscle groups since legs can be hit relatively easily with big compounds like oly lifts, squats, SLDLs, etc. while you need tons of exercises for an upper.