Now, on the second challenge.
So you need to wait for the calculated day to send a reminder email: some sort of "Today, XXX has been working for 3 months since its first day in the company", right?
If so, I believe you need to store the info from Forms response somewhere (Excel table, Sharepoint List) and design a second Flow of tipe Recurrence, frequency daily, that would read all the list elements, and for each one will compare calculated date with current executed date. A reminder will be sent for every match.
The reason for a second flow is, as far as I know, max Flow execution time is 30 days, so you cannot implement all in one flow (the one that is triggered when a Forms response is received) and add a Delay action block for 3 months.
Does the suggested strategy match your requirements?
THanx!