I am recently approach by one start up company CEO to work for him as CTO.
There will be 3 person in team,CEO,CTO,CFO. My responsibilities in company would be to look after all such tech. part and give pointer to CEO about development,30hr/week.
Now my question, how much salary or equity should I ask him for joining as CTO?
I don`t think there is one right answer to this question. One way to work things out, might be to consider how much you would earn (with your current experience) in the open market and then obviously discount pro-rata (for the part-time nature). Then further, since it is a start-up discount this "salary" in exchange for equity. The equity should be based on the considerations including the potential upside, the amount of work and contribution you would make etc.
At the very least knowing what you are worth in the "open" market is a good starting point for a negotiation
Just a note of caution: all 3 of you have fancy titles. You can't possibly need a full-time CFO yet, since there is nothing going on.
That being said, how much to ask for depends mostly on the stage of the company: how much money, if any, has been raised so far?
If this is extremely early-stage, no money in the bank, it's all about equity, in the order of a third (or more).
If the company has a little bit of funding, salaries should be set to provide enough runway so that the company doesn't run out of cash too soon (18 months of cash is a good rule of thumb). balance equity and cach to make it worth your while.