just in case anyone else is considering doing this..
i've tried it out, and it all seems to be working ok... ( didn't expect any problems, but you never know...)
including with markasjunk and managesieve plugins enabled.
used @kenanng's instructions for managesieve
now going to try adding kolab calendar to it..
previously had this working on global webmail, instructions here.. so not expecting any issues..
one thing to note.. completely unrelated to switching from sqlite to mysql..
can't change user password in roundcube interface when logged in using SSO... wrong existing password..
considering the way SSO works, i'm guessing there's not really going to be a workaround for that..
i am expecting users to whine that they can't change the password there, despite being only a click away from managing the user account where they can change the password directly in the enhance panel when they clicked the webmail SSO link.