Our apple tree wasn't doing much of anything (it barely even ever flowered), so I finally cut it down and bark grafted 3 different varieties onto it - Liberty, Ashmead, and Cox Orange Pippin. These should all be able to pollinate one another. We also have a Honeycrisp tree nearby that should benefit from this, too.
Yes. I also like Golden Delicious, but def better off of a tree (I feel like pretty much anything is).
Have you had an Opal apple? It's a cross between Golden Delicious and another variety. My current favorite apple.