Most will tell you that you cannot successfully glue acrylic to glass due to the non-adhesion of silicone and acrylic.
That being said, I've siliconed acrylic baffles into my sump with no problems for the past 5 years.
You need to use at least a 1/4" acrylic piece, this will give the baffle some rigid form and use aquarium silicone.
I have also siliconed acrylic baffles into my sump with no problems. Just make them snug, not so much that it breaks the tank...
They will be fine.
DON'T USE GLASS. You might get a nasty cut when working in the sump.
Not if the edge is filed down and beveled, which is easy enough to do. Unless you have the acrylic laying around collecting dust, there is no reason to use acrylic.
The one thing that no one has asked (myself included), is how big is the sump and baffle. Silicone will work to hold arylic into place on a small set up. On a larger sump it will eventually fail.