There are some very good points there, I would like to give you some tips as well.
I have gone down the Yahoo Group road, its an easy way to turn clicks in customers though it takes a little effort to get the group set up right. Its really important you restrict who can post links, files and images or your group is likely to end up as another piece of cyber junk.
another tip is to have two yahoo ID's - one to promote and manage your group through the second one as a back up moderater of your group, why? Well yahoo will shut you down for using their groups for porn if you are lucky they will just ban you ID like they did mine, trouble is now I have 4 groups with about 30K members which have no moderater.
I also run this
http://www.smithslookup.co.uk/forum/index.php which is basically a links exchange for adult groups, I started this as the surfers know where the good groups are so its handy to get them to post them.
So heres my basic fomular for making a Yahoo Group Pay;
1) Add content
2) Add Links to sponsors
3) Files - use the files to send basic html pages on joining and every two weeks, I send a snap shot of my home page, a dialer page, webcam page and also one to free sites.
4)Top Lists - theres 3 good ones, Groups Portal, Erotic Stuff I cant remember the other on off hand.
Other things to be mindful of - Sponsors 9/10 won't allow you to use yahoo to promote I spoke with a chap who runs Rabbit Reviews a 30K membership group and wegcash refused to pay him $2K as he was using YG.
People posting links to non legal stuff, IT HAPPENS A LOT check al messages before you send them to your users.
I allow people to promote their group within my group, if its off topic I ask them to post on the forum or in my links page there is no point sending off topic links it pisses people off.
So how much can you make from a group, on average before yahoo shut my groups I was doing about $300 per week and it was growing at a rate of about 10% each week. If you promote the group well its possible to have 10K members in less then a week. Once you get to about 14Kmembers you should think about opening a second group as you will become very visable to yahoo.
I hope this helps, this is a really good topic and it was as a result of having lunch one day with paul markham that I went down this route, he said a friend of his worked on groups for traffic - IT WORKS!
My final tip is dont make a group where people cant post - WTF is the point of making a read only group - you need to get debate going as thats what will make or break your group.
I will be happy to discuss this further if you wanna contact me 219458592 -
Cheers - Paul