Brownie bottom cheesecake?!
Answers:
Trust your recipe. Almost all cheesecakes call for the crust to be pre-baked. between the water bath, lower temp and the cheesecake filling as "insulation" your crust will be tender & delicious!
I'm dubious because there is only 1 recipe online, but it is on a hundred different websites.
I would bake the brownie base and then do a no-bake white chocolate cheesecake filling, mound it on, level it off and then refrigerate it until the cheesecake was firm.
Just do as your recipe says. I have made one before and you only partially bake your brownie crust before you add your cheese filling. (I don't think you could make it separately.) Hope it turns out great! Sounds YUMMY!
The water bath prevents it from getting overbaked. There is no need to bake separately in fact that would be a big mess!