I'm replacing my transom soon and wanted some advice.

One thing to bear in mind is the compressive strength of the foam core. If you have any fixings or fasteners to make through the transom (outboard motor mounts; brackets/cleats/etc.), the common practice for foam cored transoms is to locally (to the thru' fixing) replace the foam with a hard pad of plywood or timber or even a metal pad which have significantly better compressive properties and won't crush when torquing bolts. The alternative being to use a large washer plate to sandwich the area and to prevent the core from crushing.