1. Yes, depending on the venting of the existing layout.
2. All depends on the existing venting. If all vfixtures are vented separately then it doesn't matter. On a wet vent typically the water closet is not before the shower/tub to eliminate the toilet flushing sucking the other traps dry.
3. Side venting can be done as long is there isn't an operable window above and according to my code you need to be 10 feet above grade.
Your jurisdiction will help narrow the answers done, my answers are mostly based on Florida and International Plumbing Codes.