I also have a Janome 6500, that came with many feet with the machine. I don't believe it would be to your advantage to buy extra feet at this time. Like others have said, wait to you really feel that you need them.
I purchased a Teflon foot, thought it would help me sew on the no-skit shelf liner...nope. So, I to am only out the money for one foot, in 9 years.