Something that needs to be taken into consideration when you get into the world of narrowband is the focal length you plan on imaging with them. If you image with a system that has a focal length less than F5, the transimission rate of that given spectral line decreases. This will require longer and more sub-exposures. Again, if you're imaging with a 3nm filter at a focal length less than 5, your transmittance decreases. The peak trasmiittance with Astrodon filters are guaranteed >90% at F9. This is important to remember. I currently image with 3nm and 5nm filters at F5 without any problems.
The other point to take into consideration is whether you will be automating your focusing routine. Astrodon guarantees parfocal up until F4, but anything beyond that will require refocusing.
My current and future set up:
Ha 5nm (I wanted to keep the NII line because I plan on imaging planetary nebulae in the future and didn't need the increased contrast)
OIII 3nm (light scatters far too easily due to shorter wavelength ~500nm)
SII 5nm (isn't susceptible to LP and less susceptilbe to moon ... no need for 3nm for my needs)
HII 3nm (increased contrast. My plan is for mono imaging)
NIR >700nm (Image through dusty regions to highlight background galaxies and clusters encompassed in dust)