Let me give you a couple pointers of things I learned in the aftermath of my group buy.
1. Lay out your terms as specifically as possible
- How long will you host the devices?
- What happens when they become unprofitable?
- Can people transfer interest and what rules are there for this? (I advise against this.. it makes a huge accounting mess as I am learning.)
- Make sure everyone knows you are not and will not guarantee any profits and each person is investing at their own risk, and that by sending you money to order the Avalons they already understand this.
- Will you merge mine any coins? which ones?
- Will you go solo? overclocking?
- Which pool will you use? (if you do)
2. Go ahead and make some forums somewhere so you can keep everybody up to date and everything organized. Have users PM you on bitcointalk their email they register on the forums with, so that you can verify their identity. Only allow the verified group posting privileges, otherwise spam bots show up.
3. If any extra expenses are required, let it be known (rent/power conditioners/240v PDUs/C13 to C14 cables/electricity to run the A/C, etc).
4. You can use
https://github.com/csjones/sharebitcoins to make dividend payments easily.
Just really make sure to think through your terms before collecting money. Also, from experience I think 3% is too low a percentage. I wish I had charged more because it takes a lot of time and effort to manage 87+ investors. Also, you will receive your units much later than I will and difficulty will be higher. Do not get locked into doing this for a penny per month, because you will hate it.
Good luck!