I have gone through something similar. Without disclosing final terms my goal was to end up, realistically, with between 5% and 10% of the company, knowing there would be several rounds of capital raises with dilution happening each round.
In this case the company was an app company with a pretty narrowly defined target product and the preliminary diligence showed it would not take development of any proprietary software, i.e., so all components were OTS. In addition, backend and other functions were all available as services so no huge infrastructure cost either. Adequate marketing funds, based on reasonable and realistic customer churn, were included in the cash flow so while a chance that customer metrics would be worse than planned, the likelihood was low.
That being said, I started with 20%, and assuming the current and final raise is successful, then I will likely end up on the lower end of my equity target range. Vesting was done in 5% increments with 10% after two years and the remaining 10% vesting monthly years 3-5.
I had wanted a shorter vesting time but I accepted because I knew the people involved.
FYI - I had checked with several local VC connections on this and they were comfortable that the deal was "fair" to both sides. Another reason I accepted the longer vesting term.