Walker cameras are excellent, but not necessarily for everybody. They are extremely rigid, precise and strong. But they don't have the fancy geared movements, scales, DOF markings etc some people want. The Wide and XL versions are much better suited to architecture than general photography. Realistically the longest lens you can put on a 4x5 Wide is a 150. You can maybe go to 180, but not sure how close it would focus. The 4x5 XL is essentially the same but with a rigid back.
For general photography, the one to look for used would be the 4x5 SF. It is a folding design with a long bellows draw, and works well with wide angle lenses too. It has a larger range of movements (example: front rise) than many folding cameras, so it is very flexible and can be used for a wide variety of applications.
That said, apparently the Shen Hao and Chamonix cameras are very good (I have not used one but have read a lot good things) and are priced very well.
Regarding going all the way to 8x10, think some more about the type of photography you do first. Every format has its benefits and limitations and often the type of photography can tilt you in a particular direction. Contact prints can be beautiful, but there are some drawbacks to be considered (aside from the obvious things like bulk). In particular, depth of field can be a real problem. Your choice of modern lenses is also significantly more limited than with 4x5. Also keep in mind everything needs to be bigger, from the tripod to your developing trays (for example, I would not tray process 8x10 film in any tray smaller than 11x14).
It might therefore be easier to start off with a low-priced/used 4x5 setup if you haven't worked with sheet film before. The 4x5 camera will give you the chance to work with sheet film, camera movements etc. You can then decide if you like large format, and if you want to move to 8x10.
My two cents.