Ignoring the unrealistic guests (Alyson and Seth specifically) then I'd be happy with any from this list
Sam Anderson
Daniel Dae-Kim
Christian Kane
Julia Lee
Harry Groener
Larry Bagby
Bianca Lawson
Keith Carradine
Sarah Thompson
Alexa Davalos
I know Agents of Shield guests would be hard as they're still filming at that time of year so maybe somebody like Ruth Negga would be cool as I loved her in Misfits too.
Any of the writers would be awesome as Jane was fantastic. David Fury or Greenwalt would be amazing as would Marti Noxon
In terms of repeat guests I wouldn't be unhappy with any of them. Every guest I've met at an HW has been amazing and lovely so there's nobody who'd be coming again who'd disappoint.
This post was longer than I originally intended...