I think one thing to keep in mind is that most iterations of the advanced reproduction types (this and others) have the assumption that you will be able to start the next generations with several cells instead of just one. And personally, in that case to compensate I would recommend increasing the total amount of “growth required” for reproduction to unlock after growing all cells.
In that scenario:
Starting with more cells would shorten the overall lifecycle by skipping the “slowest” part of the growth cycle.
This on the other hand would keep the gameplay generation time more consistent if you change the number of cells you start with.
With that I am slightly leaning towards option 1 for being more interesting, but I could easily see the argument for 2 if we want to keep generation times more consistent. (For example to compare with how long auto-evo takes).