Aspect Ratios & Scaling Suggestions and Advice?

[D-Dave]

I've been reading through information concerning aspect ratios (Storage Aspect Ratio, Display Aspect Ratio, Pixel Aspect Ratio, etc.). Though the concept of aspect ratios makes sense for analog sources since analog dealt with samples rather than pixels, I'm not sure how to interpret this information for digital sources (DVD & HDV tapes). There are a few scenarios that I'm trying to figure out the appropriate way of dealing with odd pixels (as well as resolutions).

If I was working with footage from a DVD and my goal was to simply tidy up the footage and store the footage on a hard drive, would it be better to keep the SAR flags on the footage or to scale the footage to a square pixel resolution (720x480 to 853x480)? I'm not sure whether video players treat SAR flags any differently than video being scaled on a display. Now if I had footage (DVD, VHS, DV tapes) that will be upscaled to 1280x720, would it be a better decision to apply the filters before or after upscaling? In regards to the upscaling, would it be wise to use NNEDI3 to get the footage close to the desired resolution and then adjust with either Spline or Lanczos?

Moving onto HDV footage, if I was to edit my 1080i footage and keep it as 1080p (most likely deinterlaced at 60 fps), how should I deal with the SAR of my HDV footage? Would it be wise to upscale after deinterlacing but before applying filters? Lastly, if my output for the HDV footage was going to be in 1280x720, I was thinking of doing all my work at 1440x1080 then downscaling to 720p. Would this be better than correcting the odd pixel ratio by scaling to 1920x1080 before editing?