I manage orchestral music using a variety of sample libraries which requires a fair amount of midi manipulation in Reaper and it's just fine. The likes of Cubase and Logic, by all accounts, do it better (and have handy things such as articulation mapping etc.) but it's entirely possible to do, and without any tweaking or add-ons.
Personally I have 3rd party plugins for EQ, compression, reverb etc. anyway, and a many people say Reaper's stock plugins are good (I'm not convinced myself) but yes, you may wish to buy some 3rd party plugins or grab some of the good free ones about. Melda have some good free ones if I recall correctly?