The growth your vine is putting on now will have the flowers, and therefore the grapes you'll want later in the year. The new growth will continue throughout the Summer, and you can prune much of this back if it becomes excessive without harming the vine.
As far as reducing the size of the old wood (the bit that looked dead in the winter), vines respond very well to hard pruning during the Winter. I hard prune my vines back in January, removing 90% of all the growth from the previous year. This will leave you with a permanent 'stock' which will produce plenty of new growth in the early Summer. The size of this 'stock' will determine how much growth, and therefore fruiting potential you will get. The less growth you have, the better chance you'll get good sized grapes which will ripen properly, so if grape production is most important it's often good to prune very hard back to a short stubby stock. Really huge vines are excellent for appearance, or shade over a pergola, but often struggle to ripen the grapes properly. Growing in a greenhouse will of course help in this regard.
Cheers, Mark |