Hi Dennis,
Ah the famous MSU fertilizer. Before I moved to Australia I lived in Michigan, only about 2 hrs from MSU. We'd regularly see jaw-dropping plants form MSU brought in for shows and judging. Amazing stuff.
Anyway, I'd say a 25-inch leaf span on the Vanguard/sanderianum cross is near blooming size if not blooming size. I don't grow many sanderianum hybrids so I am not familiar with their bloom triggers as I am other plants. I can say they like a little more light than other paphs. I have a straight Vanguard about the same size as your cross I am hoping will bloom in the next year or two.
The Black Brier cross should be pretty easy to grow and bloom as it is one of the intermediate-warm, low-light Paphs. I find these very easy to grow and bloom. They do well in an east window or under florescent lights, and they can clump nicely when they are more mature giving you more blooming size growths and therefore more blooms. I love these dark vini-coloured Paphs and have about 6 or 7 different crosses.
I like your taste in Paphs. Check out the Slippertalk Orchid Forum at:
www.slippertalk.com. It's like this forum except all slipper orchid talk. If you haven't yet, go to the American Orchid Society website and get their culture sheet on Paphs.
Keep asking lots of questions and happy growing! If you get a chance, post pics of your paphs when they bloom.
-Kevin