If the tractor is in good shape, I'd say that you did okay (A new FEL starts out around $3K and goes up from there...).
The "e" indicates that the tractor is a 2wd. There will be times that you'll wish that you had 4wd, because with a heavy load the rear-end can get light causing potential traction problems.
The only other caution is that, if I remember correctly, the B6000's rear PTO turns in the opposite direction from most tractors in the United States (including most other Kubotas). This could be an inconvience when shopping for 3-point hitch PTO equipment.
Kelvin