Sounds like you have a plan. I would leave everything as it is with the two orandas in the 28 bow. That will give them plenty of room, I think. You might want to add Brig for color and to scoot around your tank, but goldies don't always treat snails with the best of intentions. Great save, and we'll look for pictures of the happy duo once you get everybody acclimated.
A brigg might be fun. I've had bad luck with them lately. I was also considering nerites- the store where I got the new oranda has some reddish spotted ones.
I'm going to wait until after I finish treating the goldies though.
I'm not sure of the dimensions of your 28g, but I have 2 29g's, each w/ 3 fancy goldfish. A little overstocked, but very well filtered and they get large water changes at least 2x a week. It's working very well. We have goldies in bigger tanks, too. Both my husband and I really love goldfish AND, I know I'd love to find a blue oranda at some point