Hi,
One of those Astrozap or Baader pre-made solar film cells would be fine (ND5.0 is visually safe). You could get one for the full aperture at 150mm and be ok. Just use low magnification when seeing is really poor. Consider green to red wavelength filters to handle seeing.
To make your newtonian work with h-alpha you would need an expensive etalon filter system and it would require energy rejection since it has obstructions (your newt's secondary) and since mirrors absorb heat and do not fully transmit all the energy. This is also expensive. It would be more difficult and costly to turn your 150mm newtonian into an h-alpha chromosphere capable instrument than it would be to simply get a small 60~80mm refractor and an h-alpha system for it (or a dedicated smaller instrument).
Night time h-alpha filters do not show you the chromosphere, they're too wide bandpass and will only show you the photosphere. To see the chromosphere you really need to be less than 1 angstrom bandpass (0.1nm). So 3nm, 7nm, 12nm, or more is too wide. It needs to be down below 0.1nm. This is why etalons are used.
Check out the forum stickies to get more information on etalons and why all of this is needed.
Very best,
