i didn’t see the part about freeze frame, oops…As for 60 fps, it allows for better slow motion and freeze frame effects with less line twitter. There’s more information, basically, but you would have to work in a 60 fps comp to keep the information or AE might interpolate each frame back into a field again.
you must mean 864×486 NTSC D1 Widescreen Square Pixel uncompressed SD; to stretch a video back to widescreen after it gets “squished” when you export it from a system that doesn’t understand pixel aspect ratios.
you only need frame blending if you are doing frame rate changes, and if you did, pixel motion is way smoother than frame blending anyway.
The compositions pixels aspect ratio setting should match that of the final output format. So keep that in mind.