here is the answer (I hope):
personally, I own only one 5nm filter now as I already sold all other 5nm filters I ever had due to an upgrade for 3nm set I would always recommend 3nm OIII, 3nm SII and based on your budget decide between 3nm or 5nm Ha (I own both 3nm Ha and 5nm Ha as the 5nm one also covers the NII line found in few planetary nebulas).
do not worry about mixing different bandwidths (unless the difference is too big like 35nm and 5nm filter) it's all question of post processing where you can do wonders (if some filter produces bigger stars then the other one, you can deal with everything in Photoshop).
For NB imaging I own a CCD camera with ultra low readout noise.
For HaLRGB imaging I own a large format low sensitivity high noise camera because LRGB imaging is far different from NB.
hope this helps
BTW the fastest system I use is F/3.6. For F/2.8 I would think of 5nm filters for "safety" (Ha and SII, keeping the OIII at 3nm)
Edited by Konihlav, 20 May 2013 - 12:56 PM.