hyd - tbh, ive never tested the dofollow/nofollow ratio but I could test it if you are a motivated buyer.
You can use as many URLs/Kwds as you like.
Finally, in this day in age with Matt Cutts making these bold statements, I would be extremely careful with any links that you build to any site. That being said, I do have quite a few customers who send these links to their tier 1 sites - what I see most of them have in common is this:
1. They have very large sites with a ton of veloity (they do links all the time and have natural links going to them all the time)
2. They have a huge link history
3. Some, not all are using these just to rank in Yahoo and Bing
also - I do have high PR/edu (smaller) packages for those who aren't ready for my larger packages, that arent as risky for smaller sites
any other questions, please let me know!