All 3 machines are very different although the computer part of the 200e and the 350 are the same. The 400e and the 500e are basically the same machine. The biggest hoop for the 400e is 8" square and for the 500e it's 8x11" for doing quilting. The 400 and the 500 also have a large color screen. The 400 didn't come out in the US until well after the 500 came out. Janome hasn't even really advertised the 400, not like they have the 500. The 200, 400, and 500 all have the same way of attaching the hoop to the machine.
The 350 is a very different machine. it's largest hoop is a 5x7. The hoops attach to a bar that come out of the back of the machine, this makes it possible for the machine to have a free arm. It's not a small free arm but it is one.
If you're planning on going to the Bernina with embroidery then the 200e is a good starting point, but I like having separate sewing and embroidery machines so I can do both at the same time.
Here's a page comparing the Janome machines:
http://janome.com/en/machines/embroi...ry-craft-500e/
Cari