No, there is no roller brush. It just has an opening for suction.
#2 Can I use this vacuum to clean venetian blinds?
It will depend on the blinds themselves. There is an attachment that is include you may be able to use to help clean in between the blinds and small areas.
#3 Does it lay flat to go under a bathroom vanity and will it vlean under a baseboard?
The handle can lay flat but the suction head will not in that position; only about 45 degees.
#4 I have 2 cats and theres always a lot of litter over the floor. Will this vacuum help with that?
This is a lightweight vacuum. I purchased it for our camper for light jobs. It may pick up your litter and it may not. I would say that it possibly would, just not a large amount at one time.
#5 Can I use this to vaccum under my bed and sofa?
Yes, if you move the the bed and sofa. It only goes so far...
Sort of. As far as I can determine it will stand up by balance only if the floor is level; otherwise it tips over. Unlike full- size vacuums, when you hold it upright it doesn't "catch" or click into place to keep it upright on its own. I just lean it against a wall or something.