If you are certain you will only ever do landscape work (infinity focus, modest wide to modest telephoto), a Speed or Crown Graphic or other press camera will be fine. If you want to focus close, get really wide, shoot the occasional building, still-life, or portrait, you should seriously consider a field camera. If you're not sure, get a field camera. Better to get the right tool up front, than buy one, build a system around it, then find out that it won't do what you need it to do.
If you are interested in primarily black-and-white work, I'd look at a 5x7. Since you already have the enlarger to handle 5x7, go for it. If you ever decide to try contact printing, 5x7 is a very nice size. While 4x5 is more common, and the equipment is more compact, you'll very quickly find that for contact printing, 4x5 is REALLY small.
Depending on your budget, look at a Shen Hao 5x7 (I have their 4x5 model and I love it- had it for close to six years now, and it has been a real trooper). They make two models of 5x7 - one has a shorter bellows, less movements, and weighs less, the other one has a longer bellows and more movements. The smaller camera sells for about $1200 USD, and the more versatile one goes for about $1500.
When I got my 5x7, I seriously considered the Shen Hao as well, but ended up with a pre-owned Canham instead. The Canhams are fantastic cameras, but a little quirky. New Canhams are a bit pricey, so I'd suggest looking for a pre-owned one.