We have a single large hydraulic slider that is on the drivers side and contains our dining room table and chairs plus the sofa/ bed. It gives us a lot of room extended, yet you can still move around easily when the slider is in. Our 36' has a nice master bedroom with a walk around queen size bed and loads of storage plus it's own stereo and flat screened TV. No slider needed. My MH weighs in at around 23000 lbs empty.
Get whatever best meets your needs and gives you a floor plan you like. With a gasser you're going to get from 5-8mpg unless you're following the semis through the mountains with your flashers going and the Mrs out pushing from the rear.
Don't let having a slider(s) worry you. Make sure your sliders are hydraulically driven. JHMO