I recently encoded a movie in 528x480 using the standard KVCD template and it plays in my DVD player. What are the main differences between the standard KVCD template, SKVCD template and the KVCDx3 templates? What template would I use to get the best image quality at the above resolution?

Basically there is no diff between any template except min/max bitrate and resolution.

Right now my max bitrate is 2500 and I get a CQ of 79 at 528x480. If I lower my max bitrate to 1800 would I get a higher CQ. Would the image quality be better with a higher CQ at a lower max bitrate or vise versa?

If you compare the two results (same file size) you would see no difference in the image quality between (lower Max Bitrate-higher CQ/ higher Max Bitrate-lower CQ) and remember the lower the max bitrate, the faster you will get diffuse, bad Pictures on motion or in complex szenes.
The only thing you should change is the cq

This would be a great Quality also without a AVS Script. I think you can choose a higher res like 544x480 and you CQ fall to ~75 and I think it lokks great.

I tried 3 different sources which gave me various CQ's, 79, 74, 64. Haven't had a chance to burn to CD yet to test out the image quality. If I don't use a AVS script would it be faster to encode?

are you using tmpgenc 2.59?
This version is buggy so the filesize will be to large

Nope, v2.521. I think you misunderstood, I encoded 3 different movies with 3 different CQ values, not 1 movie with 3 different CQ values.

yes, ...but not means that you get better quality and less size!

Like Jorel.

I think,for me, the most important point is the re-zisen. So you can see more of the movie and the CQ getting higher.

And with some very good Filters you can make your source cleaner.