Congratulations Tim- we look forward to seeing your images taken with your new gear
I would also pick a mono over osc any time
As for combining filters- I think experimenting will allow you to optimise your particular setup, but I personally would avoid using two filters at the same time (reflections?). Also, I do not expect there would be a significant difference in data collected through a cheap CLS and a cheap Lum filters.
Having said that, I would hold off and save for a good Lum filter, as it plays a vital role in collecting quality data for the final Tri-colour picture.