The guide bushing sounds good . Can you rec. a bit to use with that
Thanks

I like a solid carbide spiral upcut bit, but they can be a little
expensive. You can try a solid carbide end mill - same thing, cheaper
price when it doesn't say "router bit". Check the archives for
sources.
A straight bit would work fine too, but most aren't intended for
plunge cuts. You could start it with a hand-drilled pilot hole or
something like that.
Andy