Only being one yr vine there can't be much old growth, what a foot or two? It will only fruit on canes that arise from the wood it grew this year. So save one or two of this years canes about 5-10 buds each. When those buds push the canes that form will set clusters. I'd save no more than about 4-6 clusters next year.

I've found grapes overly vigorous in my greenhouse if planted in the ground. In pots they can be controlled. Mine in 12 gal pots bore about 4-6 clusters the second year and 10 the third. That's as much as I'll leave going forward.