Dark skies if possibly are always the way to go.
CCD's can be on the expensive side especially compared to your current setup.
Although I have never used a LP filter, I wouldn't from what I have heard which appears to be the same as you.
With the HaRGB, you do only get 1/4 of the signal so it can take a lot longer to get the data but it is better than nothing right
My understanding is that you are going to need 2" filters with a DSLR. Although you can get away with 1.25" filters with some of the similarly sized CCD chips (KAF-8300 comes to mind), the filter is considerably closer to sensor and even then it is usually recommended to get 36mm to avoid vignetting.
With your DSLR, just take your normal RGB and then extract the luminance channel and blend that into the RGB data. Being a OSC there is no way to capture true luminance data.