Well after 20K I would think you would need new chainrings.

You need to match BB to frame and the cranks you choose. The spec you listeded give the BB specs of your current BB as"Bottom BracketShimano BB-UN52, 110 mm spindle BB Shell Width 68mm English" The last two items, shell width and threading are most reelvant to the frame , you need a BB for 68MM shell with english threading (pretty standard). The other stuff, spindle length and type, will be detrmined by the cranks you choose. Your current cranks require 110mm square taper spindle. If you go with new cranks, the type of BB you need wil change