I just picked up a Busch Pressman C (2x3 version) but I've learned some things about both in my research.
a) Really no right answer to that one. Don't go thinking the only way to shoot landscapes is with short lenses. Sometimes a long lens is what you need. So, a short (~90mm), normal (~135mm) and long (~250) would be good. Obviously it will change depending on the focal length you like working with in whatever format you shoot right now. I prefer normal to short telephoto, so I have an Optar 101mm and Kodak Anastigmat 170mm right now, both picked up for under $35. I don't care about anything being top of the line or tack sharp, because this camera is just for fun to me.
b) If you like 35mm focal length, then look for a lens around 100mm. But, be careful whatever lens you get covers 4x5 because there are many 101 and 105mm lenses made by Wollensak and Kodak that were made for the 2x3 format. This was (is) the hardest part for me about finding cheap lenses. Not knowing if it will cover the format. If you find a lens you think you'd like, do a google search and look in this forum, photo.net, and largeformatphotography. Chances are someone else has asked about the coverage of that lens.
d) Look at the Graflex viewfinders with the drop-in masks for different focal lengths. Or, if you're using a normal lens, use the sportsfinder. If your camera also doesn't have a rangefinder, you'll either be focusing with the ground glass (in which case a viewfinder isn't necessary) or hyperfocal distance focusing. But, you talked about wanting shallow DOF so by definition you will probably not be using hyperfocal distance focusing.
e) There is a seller on ebay who is also a member of photo.net that sells the 4x5 lens boards. His name is Gary. Unfortunately he does not sell Pressman C lens boards, but that doesn't matter to you, only me! Search "Busch Pressman lens board" and you'll find them. I think they're $22.50 each and he'll drill them in #0 or #1.
I got the 2x3 version because my enlarger can handle 2x3 but not 4x5, so 4x5 would not do me much good. But, once I can start enlarging 4x5 I think I'll be getting a Pressman D. They're fun little cameras.
P.S. These cameras use spring backs and are not directly compatable with Graflok backs. Not an issue if you just use sheet film holders. But, if you want to shoot roll film, you'll need to get either a roll film adapter like an Adapt-a-Roll (which I'm still trying to find in the 2x3 size) or Calumet made one too. There is an Adapt-A-Roll available as Buy-it-Now right now on ebay that will fit your camera.
Have fun!