There are several of us vegetarians here successfully following this plan. The plan recommends that you start with 1/2 of beans as a serving, but you may have more than that if you prefer. I wouldn't be concerned about the calories in the beans, but you do have to limit nuts since they're high in calories. Check out the guidelines in the Phase 1 food list for the amount you may have for each type of nut.
I also get my protein from some vegetables, cheeses, and, occasionally, tofu.
I hope you join us in our Daily Thread, and look forward to getting to know you. Good luck!