sorry, forgot to add: 5) My understanding is that it hasn't bloomed in years. what do I need to do to get the guy to show happy flowers?

1) should i re-pot it? If so, do re-pot before or after the trimming party.

I would personally repot it, since you probably don't know when the last time the medium was freshened, and it hasn't been blooming in years. The pot size looks appropriate to the plant size, but if you pull it out and it's pretty root bound, you can go up one size and put some fresh medium around it. You will want to use a medium with very good drainage, for example, a blend of equal parts peat, perlite, and bark.

2) Are the yellow leaves a sign of distress, or just a healthy color variation?

Do you know where this plant was hanging before you had it? Was it outdoors? Hoya carnosa leaves do become more yellow-green when exposed to high light. For example, here is a photograph of one of Pepeuve's Hoyas, which receive strong outdoor light in Malaga, Spain.

You can see they have a very light green color, too. It's hard to tell shades of green from pictures sometimes. If they aren't falling off, and the vines still look healthy (not shriveling), then you probably don't need to worry. What direction is it facing now? Does it have any shade? Most Hoyas do best in filtered light when outdoors.

3. Can I cut it way back to round it out more from the crown, or is this strictly a long trailing plant (see picture).

Yes, Hoyas are long trailing plants. You can cut it back, of course, but most Hoyas don't really get terribly bushy, and yours is about as full as a carnosa can be expected to get. They do branch, but they take their time doing it and the end result, of course, is simply another long vine. The clustering of nodes, like you can see at the rim of your basket, is about the most a Hoya will do in terms of fullness and they do that pretty spontaneously. There are, of course, Hoyas whose internodes are shorter, so they end up looking fuller, but carnosa is what it is.

4) Can I cut back the flower vines?

By this, do you mean can you cut back vines with peduncles (the structures that develop flowers, seen ) on them? As you are motivated to see flowers, I wouldn't do that. I am probably not understanding what you mean by this question - could you clarify?

5) My understanding is that it hasn't bloomed in years. what do I need to do to get the guy to show happy flowers?

It's weird that the Hoya stopped blooming, so clearly its needs weren't being met in some way. Perhaps, there was too much build up of deposits in its pot and giving it some fresh medium will kick start it. When you have it out of the pot, check out its roots to make sure they are looking healthy and the yellow in the leaves is only from high light. Be sure to feed it weakly, regularly, with a balanced fertilizer. Give it light that is good, but not too stressful. Hopefully, after it's settled into its new habitat, it will reward you.

Good luck!

GG pretty much covered it. Only thing to add would be check if both the hot and cold taps are softened, in the upper midwest they like to put both lines in the softener and it does yellow out and slow kill the plants, try to use rainwater etc. Mary