Ok - it's a good start
The shelf is a good shelf. You don't need to go with a theme at all, I just know some people have something in mind sometimes. Just suitable items and work out what will fit where
. You don't even need to get a different shelf later, if the layout works for you, it's fine. I have that cage. The only reason I went with a different kind of shelf was I'd had a previous cage that had a shelf across one end instead of a corner one so wanted to recreate the same set up. But no need to buy extra shelves to replace it with. Sometimes adding the odd smaller shelf at the opposite end can help as it gives a bit more overhead cover.
Anyway will wait till your list is here!