Yes to all the above comments, and just wanted to add that you sometimes can’t re-beat a custard set with gelatin like you can a buttercream, it’s a different animal. You could try working with it during the first hour or two, when the gelatin has thickened the mixture enough to make it spreadable but has not yet set up as firm as it will eventually get. Then you store/chill the cake while the gelatin continues to firm and you have a nice slice-able presentation.
Definitely use a buttercream dam, as Jeanne points out, in case the custard is too soft to support a layer above it.
re: putting fruit in a filling, I generally put down a thin layer of filling, layer of fruit, then top/fill in with more filling. So it’s all one layer, just applied in three parts.