It is not neccesary to hand baste , after you have spray basted. But the edges sometimes lift , and I do pin the perimeter. If this is a project that will be "handled" alot in the quilting process , you may get some "lifting" of the layers. I suggest you try first on a small project. Humidity will effect the adherance of the layers, since the spray is water soluable.
I would suggest of you do get sidetracked to put the project in a rubbermaid type tub.
The brand I like is the 505 spray( carried at quilt shops) but have also had good success with the Dritz brand ( bought with coupon at JoAnns).