Wanted to add my experience with Reliance here - Fabio did we have a brief discussion on seedless grapes this past summer on Instagram? I think you didn't end up planting Reliance, no?
Reliance grapes are quite possibly my favorite of ALL fruits for flavor, and I'm an apple girl, so that's saying something for a grape to beat out, say, Ashmead's Kernel, for me. Our customers also adore them. HOWEVER, their purported "reliability" in zone 5 has not proved to be true at our site. Since planting them in the late 80s, we've had to retrain them up very frequently due to die-back from cold damage. Trunks and all. They also have a hard time handling mildews and anthracnose. Wasps love them and have a very easy time slicing open their thin skin.
Suffice to say that if they weren't so amazingly delicious, we would have ripped them all out years ago. Glad you've been having luck in the greenhouse, Todd. Having a greenhouse is a dream of mine and as soon as I build one I will stick some Reliance vines in there.
For a commercial operation that needs a reliable crop of PYO seedless grapes in Zone 5 (we are 5a), I'd recommend Mars. They've done the best (with cold, disease resistance) out of the handful we've tried. They ripen a bit later than Reliance, but should still fit into your apple season well. Looking forward to hearing your experiences with the varieties you chose.
The UW has a seedless planting at their West Madison Research Station (also zone 5a) - they had good luck with Reliance until the winter of 2013/2014. I believe they lost all or most of their vines. Same for Canadice, Vanessa, Venus, Jupiter, and Thomcord there that year (according to info I have written down from a 2015 seminar). There is now more extensive research/breeding being done on cold-hardy table grapes at the University of Wisconsin - River Falls. Hopefully they will come up with something wonderful.
Meanwhile...I put in 6 Saint Theresa vines this past spring. Hoping that they turn out to be our new favorite!
Door Creek Orchard
Zone 5a in Wisconsin