Sounds to me as if you are trying to screw over your friends, or simply use their capital to make yourself some money at their expense. Besides everything else you posted that diverts the lion's share of profit to yourself, after 9 months the GPUs will be worth a lot more than 10% of their original value, so sounds more like a final exit scam on your friends.

I cannot discern how many friends you have from your post, but for sake of arguments lets run through a (imho) better alternative with yourself and say 3 friends.

1: Figure out how much the total cost for the rig will be once setup and running. Divide by 4 and you each are equal investors. Agree with your friends on a setup/support/maintenance fee you will charge each month. Say 10% of the net profit (after electrical), but up to you to negotiate up-front with them the exact amount.
2. Setup and run the rig for a month. Keep careful track of profits and electricity costs. Subtract electrical costs from the total profit, and also subtract the fee for yourself. Divide the remainder (or net) profit equally among everyone 25% each. Keep good records with screenshots (at least 1x a week) showing hashrates, exchange prices, etc. so there are no questions on how you arrived at your calculations. Might also be a good idea to share with them the pool link so they can keep tabs in real time if they wish. Also, you will want the address you are mining to with the investors rigs to be totally separate from any private rigs you are running.
3. Repeat each month as long as rig is profitable. Remember your fee includes you keeping up to date on latest mining software, most efficient settings, best algorithm to mine for max profit, etc.
3. If they do want a buyout at some point, again this should be negotiated up-front, but I think with a more fair value say 33% of purchase price after a year. Maybe 10% after 2 years.

Is not a joke! I'm serious! The history of Ethereum it's a fake. The "Dual Scam System" is the real project. Search on the darknet…