The move up to MF is more than just the camera.
Don't forget you'll need a bigger spool for your tank if you use stainles steel. (some plastic ones are multi-format) You will also need the neg carrier and a bigger lens for the enlarger (I'm assuming you enlarge your own). A 50mm lens won't give you the coverage you need. You'll need a 75mm at the very least.
I started into MF with a Yashica C TLR. No builtin light meter and a fixed 80mm lens. Was OK to start with, but I wanted more flexability. Bought an Mamiya RB 67 and am happy. It has become my main camera (I still use the 35mm on occasion).
As for online camera stores I would recommend KEH Camera Brokers, based in Atlanta. I've bought 3 lens (90,150,250mm). Good service, more than fair rating on equipment and quick, well packed shipping. Wish I could help with a camera store in New Orleans (beautifull city) but I was only checking out the drinkin... I mean tourist sites when I visited.