subdomain or sections to restrict access to paying visitors - Joomla! Forum - community, help and support

guys

here's first post on subject - there's lot me try figure out i'm sure there many more follow!!

i've been trying head around best way make work - let me try explain want do....

i going start produce online learning material provided in exchange one-off payment us. there several different subjects visitors can sign for, or can opt sign group of subjects or entire learning catalog.

there structure similar around 3-4 groups, each around 10-15 subjects:

learning>group1>subject1
learning>group1>subject2
learning>group1>subject3
learning>group1>subject4
learning>group2>subject1
learning>group2>subject2
learning>group2>subject3

so i'm trying figure out whether best option use 1 joomla install , have section each group, category each subject , configure user accounts access relevant sections or categories accordingly. or whether use subdomains separate joomla installs each group etc etc.

i'm sure there other options , i'd love hear them if can point me in right direction.

i need figure out how sign process work , how allow people choose area(s) of site access during check-out process.

as can tell description of requirements, don't know start , appreciate advice can offer.

thanks in advance everyone.....