You should wait until the male has been neutered, and for 2 to 4 weeks to pass, before you attempt bonding. That’s always the first step before you begin bonding. You can keep them in the same room, in different pens. If Winnie is free roam in that room, make sure that you have an extra barrier between her and the new one, so that no one can nip through the bars. You can surround his cage with an x-pen, or with a pen made from the cube grids.
My rabbits have always shared litter boxes and food bowls, but there was not the size difference that you will have. Depending on how old the male is when you get him, he may still be on alfalfa pellets and alfalfa hay after he has been neutered and you bond them. Winnie would at that point be on timothy based pellets and timothy hay, so you might have to feed them separately for a while. Even when they are both on a timothy based diet, the Flemish will need a lot more food, so I’m not sure how you would handle that.
I have bonded 5 pairs of rabbits over the years. None of them involved bunny dates beforehand. Mine were all easy, but maybe I’ve just been lucky.