An acre pond is nice. The larger the volume of water the more stable and resistant to change. Just like large home aquariums. Smaller volume of water = more work to maintain.
Good on you to remove the old and start fresh. Definitely remove the cattails, and either eat the fish, use them as fertilizer in your garden, or give them to a local shelter of food bank (depending on the species and size of course).
How old is your grandson, or how experienced is he at landing fish? The beauty of bluegills are their hardiness. Often no bait required, just drop the shiny hook in.
You could do both bluegill and crappie in addition to the largemouth bass. But you will have to decide when you will introduce each species after you decide your goal(s) for the fish in your pond.
If you aren't concerned about growing trophy bass you could "drop the pot luck" - bluegill, crappie, channel catfish, largemouth bass, and grass carp. Some folk enjoy fishing waters wherein on any given day they land different species - not knowing what's on the end of the line fishin.
It is likely your grandson will enjoy a dock
