A few questions/thoughts.
1) Cash loan on what terms? Seems like a good opportunity to take it in the form of preferred shares, first $300K of any exist >$1MM for example.
2) Fuck the "OR", always remember any negotiation can be an "AND", cherry pick whatever terms YOU think are right.
3) Ask him to take your "friendship", and past effort, out of the equation. He has a supposedly MVP and he needs to hire the "tech guy" to build and maintain it. What would he offer someone for that role in terms of salary and equity. Don't worry about what the company can afford, pretend his rich uncle is writing the checks for him. Value the position first. What would a "normal" person expect from this role, what kind of talent does he want to attract?
From #3 I think you'll have a better negotiating view. He most likely either places no value on the position (which is a signal to you) or he recognizes the value but the lack of short-term resources to recruit properly. In this latter case, you are foregoing other income opportunities to take a risk with him. That risk needs to have a payoff above and beyond what you could get on the street to make it worth taking on your part.
Reading what you posted, 5% of a $10MM (best case, which is generally unlikely) is $500,000K. As a lump-sum that's not life-changing for most people, spread over 3 years is $166K/year, which is very nice salary (if you get it), but still no where near fuck-you type terms even in the short duration.