My main expertise lies in :
Growing organic traffic
User content generation
Product development which drives better conversions
Designing highly scalable products which can grow with minimum funds
Have done and demonstrated product development and high user growth at transtutors.com
Build organic traffic
Build user engagement
Monetize high traffic product
Build technology which can scale
Yeah for what you have mentioned it seems 30% is more than enough.
Now it is also important to keep in mind how important is technology going forward. If your business is totally tech dependent for example ad-tech or artitifical-intelligence then 40% is good. But if your business has considerable amount of offline work for example ecommerce, getting vendors and partners on platform then 30% is more than enough.
Finally if you are going to be CEO and other guy is CTO and he gels well with you and works with complete alignment of goal then you can consider giving him 40%. Its pretty hard to find awesome tech guys these days. And more than that if he realizes to work with you as per your plans then its very very helpful.
We can also chat in detail if you want.