There is a lot than can be done. It really depends on your wallet. I would start by getting the thing to run. This will give you a base line for how well each enhancement is or is not working. 90 to 100 hp can be realized (this was factory for the 885 in other models). Personally I'd start with the exhaust
staintune or
thunderbike. thats stage 1.
Stage 2 .. 3? link is for Wilcox who seam to have some fans and detractors. regardless illustrates the next steps well. it is also possible to go bigger with
955 liners. Also seen different igniter (higher rev limit) and coils.
NOTE all this is conjecture on my part as I am only seriously thing about exhaust and the only for acoustics than performance. Current I can keep up with the Sport bikes and don't think twice about Harlys/Cruisers.