Although I've not had my 4x5 out for several years (sigh), I'll second the recommendation of a good field camera, preferably one that folds up into a nice box. If you want style points, look for a cherry or mahogany camera.
My 150 was my most used lens, followed by the 90. You can save considerable money buying slower lenses, which are lighter, and since you'll be shooting at very small apertures anyway, it doesn't much matter. A 150/5.6 and a 90/8 are a fine start, and will provide years of use. When deciding which lenses to buy, think about your most used lenses on your 35mm and MF kits, and work from there. If you like really wide, look for a 65 or 75. If your favorite lens is a 28mm, then the 90 is good. If you like the sort of "wide normal" lens preferred by a lot of rangefinder shooters, the 150 is an excellent choice. Etc., etc.
I think Fuji still makes instant sheet film in 4x5 to fit the old Polaroid holder. It's not cheap, but it does provide instant feedback when learning how to set movements on the camera.
Have fun! It's a whole new world...