Good advice from everyone else.
I have done beading on cross stitch pieces just holding the work in my hand, usually when my scroll frame is in use with something else. I would not try to put Qsnaps over beads.

Although tedious, it is best to stitch each bead on with a cross stitch, as this ensures the bead sits firmly just where you want it to be. If you have a long line of beads that are touching each other, then you can stitch 3 beads at a time using beading back stitch. Some tutorials say you can do 5 or 6 beads at a time but I find 3 gives me more control over curved lines.

And I definitely stitch at a table using a terry towel as a cloth. Beads like to escape from their little containers and jump all over the place. Terry towel keeps them controlled.

And finally, use glass beads. When I didn't know anything about beads I bought some plastic ones by mistake. Plastic beads break during stitching and melt if an iron gets anywhere near them.

Have fun, Annette