The easiest (and best actually) way to better understand what mod is doing what is to set up a local install of our SEO premod
Then you'll be able to decide which mod you need and want if you really want to go for standalone installs, or if you just want to go for the premod (since it's the handiest solution).
The minimal SEO set up would be SEO url + zero duplicate, then optimal titles, meta tags and no dupe (in this order of importance, but they are all useful).
GYM sitemap & rss is as well kind of a must have as soon as your forum gets a bit big. And of course, all of our mods are compatibles with each others, only the zero dupe and the no dupe requires one of the SEO url mod installed before you can actually use them.