yes with vents1. Can I hook the tub and sink into the toilet drain or does it have to run separately?
vents are needed. if you don't when you flush the toilet upstairs the trap for your fixtures down stairs could empty and cause your basement to smell like sewer .2. Does it all need to be vented or can it do that through the main stack?
you need a pitch of 1/4" per foot.3. How much slope and therefore how high would the floor have to be to make a 5' run?
you would be much happier opening the floor. It would be much nicer looking if you just open the floor.4. As long as I build a solid floor (7/8' plywood) and theres no flex, is there any issue with building on a wood floor thats over concrete?