There is no one-size-fits-all rule for setting up a partnership. (Other than you MUST have some sort of written contract in the first place.)
I would suggest that all of the partners need to work together and agree on the valuations for the assets (money, domain name, computers, etc.) brought to the partnership. The more intangible assets (SEO experience, people skills, etc.) will be harder to quantify, but do need to be taken into consideration.
They also need to agree on the value of the work each will be performing for the partnership. If you're going to be paying yourselves a salary from the start, that's pretty easy- just agree on salaries based on the work you'll be doing. If you won't be paying slaries right away, you'll need to setup some sort of "fake salary" that you build up and use for determining the profits once you start making money.
You should also have some sort of "divorce agreement" written into the contract. Who gets the domain and other assests if one or both partners decide to leave. What about the leftover money? etc.