Best time to transplant is during the winter months when roses are dormant.

Does your pruning question refer to transplanting or normal spring pruning? Pruning height depends on the type of rose and even the particular variety, on degree of maturity, on winter damage, on how much bare-leggery you will tolerate, etc. For spring pruning of established hybrid teas and floribundas, I take them to around 18" in spring. Don't prune in fall.

What Michael said unless you're talking about pruning them to move them. If they are very large roses it may be a good idea to prune them back a little to move them. No matter how careful you are you will probably lose some of the feeder roots when you dig them up. Cutting them back some will place less stress on the rose to supply nutrients to a big bush when it has fewer roots to do it with. Climbers in particular may need to be pruned down since those canes are so long. A smaller root ball will have a tough time getting water and nutrients all the way out to the ends.

But, I do agree with Michael that fall is not the time to prune roses if you are in a cold climate. Is there any way this move can be put off until early spring? In the early spring before they leaf out you can prune them back and move them with little problem. They'll wake up in their new spots and just begin to grow from there.

What seil said.

But to answer question 2, if you prune HTs low, you will have green leaves nearly to the ground, but you will have a small plant in May-June and thus fewer blooms. It may catch up in late summer. If you prune HTs high, you'll have mostly bare legs up to that level, but a bigger plant and better first flush. Very low is 8", or to the ground if there is severe winter damage. Very high is 36"-40".