This is all common when you can't afford to pay salaries. First let me get out of the way that you can not pay anyone a finders fee for raising of funds, it is illegal unless you are a registered rep under SEC rules. Although people will argue it's been done, stay clear as it will come back and bite you later.
I can tell you from experience that straight up referrals or "soft leads" are problematic unless you are dealing with "C" level relationships that can pass their relationships on to you, that you can close a deal with. Typically C level folks that you know will be happy to make an introduction. Some folks will take an under the table 5% of the first years revenue on the deal you close but again it jeopardizes the "C" levels position unless they are an owner of the company, again you need to be cautious here.
There are no best practices here just a plethora of suggestions that you will get across the board. Know you margins on the product or service you are selling and what vertical you participate in and carve out a percentage that you can live with first. Keep in mind that if is its software or SaaS your margins are high, if it's software development or augmentation its around 45% margin typically, hardware 30%ish, I won't speak to real estate or affiliate marketing as that is all over the place when it comes to the numbers.
Never handcuff your fees forever. They should only apply to the first year of revenue in my opinion unless the person referring your service helps you close a long term contract. The more someone helps you get the deal the more $$. Remember that once you install a sales organization you are going to have to deal with territory and account issues. You can't pay someone 10% on account revenues for the referral and install a sales person to manage the account and pay them a salary plus commission.
So bottom line there are no rules just suggestions and boarder line benchmarks.
And here my suggestion... 10-20 points leaning closer to 10 points if they participate in helping you close the deal. 5 points for qualified referrals. All payable 30 days after you receive payment from your customer.
Test the waters and good luck!