I have some data saved as post meta, occasionally some plugins may save an extra piece. Now I installed bbpress, it saves at least 10 pieces of post meta. Adding them together, there are nearly 35 pieces of post meta per post. I think WordPress can handle much more if without bbpress.
With bbpress forum, the number of posts will increase dramatically, multiply by the number of post meta, it will be a huge post meta table. Will it be a problem?