1) SID is the session ID variable, used to keep track of user sessions on the forum.
It is usually stored in a cookie, but can under some circumstances (after login for example) show up in url.
There is no real need to activate the SID removal option since there is in all cases no way to see and url indexed with the sid in it. The option is mainly there for users who cannot believe that bot will not index them while they see some from time to time.
2)highlights is the variable in which the searched words are stored to be highlighted in posts, example :
http://www.phpbb-seo.com/boards/phpbb-s ... ght=premod
Problem with these is that they are duplicates of the sams url without highlights.
The good thing with the dynamic meta tag mod, included in the SEO premod, is that it will output a noindex,follow meta robot tag whenever an highlight would be used, preventing this kind of possible duplicate indexing.
You can additionally decide to only allow logged in user to use them with the option you mentioned.
3) The zero duplicate should always be turned on, with post redirection to at least guests if you want to make sure that no duplicates will ever be indexed on your forum. The 2 month delay refers to the robots.txt implementation, which should be implemented after at least two month if your forum previously was indexed using the natural urls.
4.1) The zero duplicate will redirect all possible duplicates such as :
http://www.phpbb-seo.com/boards/is-this ... t1549.html
It does not change the links in the forum while the no duplicate will replace post urls with the corresponding (pagination included) topic url in the forum. It as well adds last topic titles on forum index.
It is activated on the demo server :
http://phpbb3.phpbb-seo.net/
4.2)Yes, if of course activated. The post redirection option is the "tricky one", read the description, it concern the way post urls will be handled.
5)If you are talking about the phpBB's cache folder (not phpbb_seo/'s one), then, you need to refresh it once installed, this can be done as you say or directly form the acp.
6)Usually I'd have advised you to now install GYM sitemaps & RSS (included in the premod), but we're about to update it, so you may prefer to wait few more days
So this leads us to "wait and see now", or even up to enjoy
