is there a strawberry perl equivalent of the 'ActivePerl User Guide'?

You may want to check out Pod::POM::Web, which according to the acknowledgements section of its documentation indicates that it "deeply inpsired" by "the structure of HTML Perl documentation released with ActivePerl" among other things. I've used it before and I did find it convenient to have a web interface for the documentation of what was installed in my Perl environment.

do I correctly gather that the equivalent of the "perl package manager" with Activestate is just "cpan"?

Strawberry Perl comes with cpan and cpanm utilities. Both allow for installing modules directly from CPAN - including modules that need to be compiled (such as those that use XS). Although I have never used it with Strawberrry Perl, it does include PPM.