Not much to add, except to say that the more cuttings you take, the more chance you have of them rooting - take, say, a couple of dozen - and if they all root then you can sell or give away.
I would say that you may have problems finding stems of this year's growth that are 12" long on redcurrant, but don't worry if they are shorter. Also, with redcurrant, some folks rub off the buds that will be below the ground and also the first one or two above ground, so that you encourage a single stem to take. With blackcurrant, which is multi-stemmed, you leave all the buds on the cutting.