Giovannino, I have done it both ways. When I was young and making wine with my Father and Grandfather and later my Father-in-Law, we blended the grapes as they were crushed (and, yes, the white skins went into the barrel along with the red). The wine was great and there was a certain variation year to year due to differences in the vinatages.
This year, I blended three juices (6 gallons each of Cabenet Sauvignon, Merlot and Sangiovese) and made an 18 gallon batch which is a variation of "Rosso Fortissimo." It is in bulk aging now and tastes great. (Maybe I am just easy to please. Heck, the worst wine I ever had was "wonderful!")
I am about to find out how blending finished wines works out. I have two "too sweet" batches of wine, one a Mocato to which I added apricot puree and one which I am calling "Chi Cazzo Sa" (Capisci l'italiano?) because I don't know what it is. I thought I was blending RED Zinfandel with Muscat but I think the bucket I had was mis-marked and was acutally WHITE Zinfandel. It had a strange color and in an attempt to darken it with an f-pack and red grape concentrate, I over sweetened it. I am making 12 gallons of OVZ to blend with it.
In your case because it is the first time for the blend, I would probably say make the two wines separately and then bench test a blend that pleases you. Once you have this, in the future, I would blend up front to simplify the process. In the end, all that truly matters is that it tastes good to you, not to connoisseurs or wine "experts."