basically what you would do is have an in general board that allows everyone view privileges
and in here you can set it to read only, if you don't want people to be able to post and then create a post with the instructions on how to access the other boards....or grant folks posting privileges to allow them to ask questions and whatnot.
then all other boards would be set up with only allowed specific groups view/post privileges
so you would have your normal membergroups and then your one membergroup that is allowed access to your private board
then you'll add a new membergroup, we'll called them "Paid Members"
and setting your subscription to change membergroups to the Paid Members
and on all boards, except for the private board and the general board, modify them and under Allowed Groups: check mark the box for Paid Members and do not check any other membergroups, unless you want them to have access.
for example I'll use one of my sites...in the first image you can see the Staff Boards, since I am logged in and am an admin....however if logged out, you don't even know they are there

if logged in as any other member (other than an admin or moderator) they are not seen....
in the second image you can see the Women's chat and the Men's chat, since I am logged in and an admin so I have access to both...however if logged out, the board is not found...there again, regular members can not see these board, these are special boards for 2 different membergroups, one named Female and one named Male....members have to join one or the other to be able to see the appropriate boards...so if someone is in the Female membergroup then they can see the women's chat but not the men's chat, if someone is in the Male membergroup then they can see the men's chat but not the women's chat....
hope that makes sense
just set up your membergroups and then modify the boards and add only the membergroups that you want to access those boards.
then set your subscription to move members into that membergroup.