It depends on how many boarders you plan on taking on. Up in nebraska I boarded my horse where I worked, and rented an extra stall to put my tack in. Never had an issue with my tack being used.. and as for using the arena the trainer was happy to share. Obviously if he was working with a horse that was just getting started, I would take myself to the outside arena, or wait for him to be done with said horse.. Usually there was no issue as my horse being in the arean aswell was considered a good training oppertunity..
There are different quality of boarders..just steer clear of those that seem hellbent on drama. There are plenty of good boarders out there that are courteous about arena sharing., but I agree on nixing the set arena times..I wouldn't want to spend good money boarding somewhere where I couldn't used the arena between 8 am and 4 pm.