Can I combine a BBL, tummy tuck and arm lift and what position should I sleep?

That is a lot of surgery for one sitting.  Additionally, you are not going to be able to sit on the transferred fat for your BBL, nor lay on your stomach after abdominoplasty which only allows you to sleep on your side or stand up.  After 5 to 6 hours your complication rate goes up significantly.

For safety reasons your procedure should be performed in a fully accredited facility or hospital by a Board Certified Plastic Surgeon who uses a Board Certified Anesthesiologist.  The surgical time should not exceed 6 hours, with liposuction aspirate not exceeding 5 liters.  Combining these procedures might exceed several of these parameters.