Re: Is indoor grape vine very hard?
The majority of a grape's strength and reserves are below the ground and grapes are voracious feeders. You need the largest pot you can manage as well as serious pruning and fruit thinning to get production from an indoor plant. That being said, I've seen some great greenhouse grapes, and you would be able to ripen varieties that would otherwise not survive or yield ripe fruit in your area.
Water deeply in well drained soil based on observed needs (leaves just beginning to wilt) and don't assume that a plant that is OK on Friday will still be OK when you return from your wild weekend on Sunday evening. You will get better fruit if you can allow the plant to cool at night, particularly after veraison (when the berries start to color up and make the move from hard little peas to something more resembling grapes). Direct sun is absolutely essential to properly ripen the buds for next year's fruit (otherwise you just get leaves).
"Indoor" in the Travena Cross Nursery listings means that the plant variety will not ripen or perhaps even survive in Cornwall, England. You would be much better off with a local supplier, who would be able to give you specific local advice.