Image Analysis Question

Please forgive my ignorance but I'm very new to photometry as well as using VPHOT.

I've gone through the video tutorials (twice!) and read the on-line help within VPHOT but still have loads of questions.  I'll try to limit them!

My images will all be from the same scope, SRO50, which is one of the AAVSO's robotic scopes.  The observing program is a single star (AZ Cas) in each of UVB.

Should I create a separate sequence to use for each of the filters?  Or is 1 sequence to use on all 3 ok?  I noticed the FWHM for the target, check and comp stars seems to get saved with the sequence.  But I've discovered if I pull up a different image than what I used to create the sequence, and load the sequence, on that image, the FWHM values are a bit different than if I re-load the GCVS and Comp Stars catalogs on that new image.  Because I have to redo all the work relabeling the comp stars as well as calculating and adjusting the aperature radius, I can see great benefit in using sequences.  However I'm concerned that I will lose precision with this seeming difference in FWHM between images.  The stars are relatively bright (9, 10 & 11 mag) and it was suggested I actually use 2.5*FWHM, so maybe the minor differences in FWHM between the images is insignificant?

Or are there clues like a significant difference in airmass that would suggest creating a new sequence?  Or should I create a new sequence every few weeks?

VPHOT is a great tool but it's so easy to click-click-click and have a report.  My biggest concern is poor data accuracy from my ignorance.

Any help or suggestions would be greatly appreciated!

Wayne Westlake