I've done Yahoo Fantasy Football for the last 4 years and was the commish for 3 of the years. I've done small leagues 4 teams and biggest I've done is 10. I like Yahoo a lot and have heard good things compared to some of the other ones (ESPN for example).
Things to decide before starting
1. League size: Honestly an 8 team league is probably the most fun. It's competitive and not too frustrating. The more teams you get involved the fewer good options available. What usually happens with a big league 10+ is 1-2 guys run away with it and 1-2 guys really suck.
2: Money: Do you want the league to be for prize or not. I've typically played in $100-150 leagues. The payouts are based on size of the league for 1st, 2nd and 3rd. Also if you want to pay out weekly top scores winners. For instance the $150 league I played in was 10 teams, 1st paid out $450, 2nd $300, 3rd $150 with weekly highest score getting $35
3. Scoring: Standard scoring format often gets adjusted in a couple ways. The biggest scoring factor to consider is if you want a PPR league, Points Per Reception, typically it can be as high as 1 point per reception to as low as 0.25 points per reception. Rushing and Receiving yards typically have 10 yards = 1 point. However, passing yards I've seen from 25-30 yards to = 1 point. The last way people adjust is with the defensive scoring 0-6 points, 7-13, 14-20, etc can be adjusted. The douchiest thing that I've ever experienced is one commish one year thought it would be funny if they had a -5 points for 35+ points. Needless to say the extra penalty sucks.
4. Draft: Decide if it's going to be an auto-draft or a live draft. Either one is fun, but if money is involved most people like a little more control of the live draft.
I'm interested to participate, depends on what you (commish) decides. If you need a commish I'd be more than happy to do it.