I would also recommend the rental strategy prior to buying as well. I am doing that right now. If school district is a priority then the Torrey Pines school district is tops, (which means you live in Carmel Valley) and other good school districts would put you in Solana Beach, Del Mar and of course La Jolla. The Poway school district serves Rancho Penasquitos, Poway and Rancho Bernardo and this is also a good district. I also like Encinitas and Cardiff but I do not know the quality of the San Dieguito school district.
Again like you I am renting and I have two toddlers and will be concerned about school in a few short years.
Mello Roos fees vary with the subdivision you choose but a good rule of thumb is that if you choose a newer home, (built in the late 90’s and after) the chances are good that you will have MR fees. When you start really looking the MLS listings will display if there is a MR fee or not.