I own an oxygen 49 2nd gen and don't really see myself getting rid of it any time soon. The keyboard definitely important, there's no point in not having it. I write all my melodic and most rhytmic parts through it, clicking with a mouse on a piano roll is very uninspiring I find.
No monitors for you which is fair enough, so a solid pair of cans instead. If you have the cash please do spend it, don't try save pennies in this department as your monitoring gear fidelity is incredibly important; I can vouch for the accuracy of sennheiser hd600 cans, although please do some research and shop around.
Software wise you seem sorted. I am to try Reaper myself soon as I've heard a lot of good stuff about it, particularly when it comes to performance.
That M Audio soundcard should serve you nicely as well.
Your computer might hold you back, what's the spec on it?
So yeah: decent computer + decent cans + decent audio interface + midi controller + daw and virtual instruments and you're set.