In earlier posts, you say that you carry the Mamiya 7II around regularly and that what you like about it is that, for the format, it is relatively light and compact. I also use a Mamiya 7II, as well as an Arca-Swiss 4x5 and Arca-Swiss 8x10, and I wonder whether the larger negative that a 4x5 camera will give you is worth the tradeoff in greater weight and bulk. Unless you want to make very large prints, or have decided that you need to make in-camera perspective corrections, the Mamiya will fulfill your priorities (unless you want to do head and shoulders portraits) every bit as well as a 4x5, with less weight, bulk and hassle.
I think that you should step back a bit and take your time on this. I'd like to suggest that you ask the gentleman that you met at the darkroom whether you can go with him on a shoot. Most people who use large format cameras would be delighted to do this, and it would give you an opportunity to use a 4x5 camera and perhaps to process and print some film.
I'd also suggest that you have a look at Jack Dykinga's book Large Format Nature Photography. It contains many examples of landscape photography, which is your primary interest, with detailed information about how they were shot. You will come away with a clear understanding of how 4x5 cameras operate and lens options. If you are technically oriented, I would also suggest that you have a look at Leslie Stroebel's View Camera Technique.
If you decide to purchase a view camera, one of the key considerations is what lens or lenses to get. As I understand it, you are using your Mamiya 7II with the 80mm lens. In 4x5, a lens around 150mm would be roughly equivalent. I would suggest that you have a look at the depth of field tables on the Schneider Optics site to get an understanding of the impact on apparent depth of field of the longer lenses used on large format cameras. The tables are at https://www.schneideroptics.com/info...bles/index.htm
. These tables apply not only to Schneider's lenses, but to those of any maker of large format lenses (e.g. Rodenstock, Nikon, Fuji). All of this said, I do wonder whether you might be better off buying an additional lens for your Mamiya, if you think you need one, or a good tripod and head, if you don't have one, than buying a 4x5 camera and all of the paraphernalia that goes with it.
Hope this helps.