I bought this land recently. How do I “improve” it with permaculture?

I recently bought a house with plenty of land in south Italy (Calabria). There are plenty of old olive trees, oak trees, fruit trees (figs, mandarines, oranges, lemons, pears) and some 70 year old grapes. I am completely new to gardening and I have been educating myself on how to do it properly.

I would like to have some more fruit species that are not there already, some vegetables, herbs etc.

What would you advise me to do?

I recently learned about a food forest but I am confused on how one can transform an existing piece of land into one. Should I just plant some smaller trees, bushes and vegetables between the existing olive trees?

Please give me some tips or help me find resources that would be relevant to my situation. Especially relevant to the Mediterranean climate.