what extra parts should i buy when i buy this Tumber new

As far as consumable parts, you wont need much extra in the beginning. There are preventative maintenance steps you can take. Which are: keeping the threaded rod clean (use a brush), keeping the wing nut in the bowl clean as well. These two things are the most important. Because once the grit starts to wear them enough, the nut will no longer hold the bowl in place. Also, don't use grit coarser than 120/220. While it would work, it would also wear out your bowl quickly, causing leaks.