Greg, the SCX takes the Cambo/Calumet 6-3/8 x 6-3/8 inch lens boards. They are made of metal and when you buy them you buy them with the hole size that is appropriate to teh shutter attached to the lens you will be using. In general, one mounts a les & shutter to a board and leaves it on the board, meaning for 2 lenses you'll need 2 boards with teh appropriate holes.
As far a lens goes, you'll get a lot of varying opinion based on everyones experiences. I landscape mostly with a 135mm and 210 mm Schneider Symar-S. Its a 1980s-era lens that is easily and affordably available. I also have a 90 but don't really like using it too much -- too wide for me. The 135 is just a bit wider than "normal', which is commonly believed to be 150mm for 4x5 format. (Opinions on that vary also... but thats another thread topic!)