If you have a router you can forgo a drum sander. You just need to build a simple jig for flattening the board after glue up.
Power planing and jointing end grain is not advisable IMO. Hard on the knives and your board can explode under the feed rollers. Power hand plane is dangerous too.
Look around for a sign shop that has a CNC router and just pay them to mill it flat and parallel. Same premise as the router jig.