My avocado likes to be watered about once a week in summer, twice if we have a heat wave. The roots of avocados are shallow, in the top 18-20" of the soil, so frequent watering is good, as long as the soil drains well. Avocados like very good drainage.

Root shallowness is also why avocados love a mulch under them, and using their own leaves is the best mulch! So just leave all the leaves that fall right under the tree.

The fruit drop could have been because of lack of water, like you suspect, but can also be from incomplete pollination. Avocados set better fruit with another avocado near by, but will set some fruit in California even without another tree, but in some years they will set better than others.

I feed mine a good citrus food 3 times a year, spring-summer-fall, that keep the leaves nice and green. Be sure to use a Citrus food, most will also have avocado on the label.

And avocados can get various fungal leaf spots, which looks like what you have. I found a spray with a good fungicide, like Bonide copper soap spray or Ortho Disease B Gon, used according to the label, got rid of it.
Be sure to spray the ground underneath also, fungal spores can hide out there. Be aware, fungicides are preventative, the spots already there won't be cured, but it will protect new growth from getting spots.

I actually only had to spray two times over a couple months to get good protection, and the next year the spots didn't come back either. But I keep a look out for them just in case.

Good luck, hope this helped.

I'd also suggest upping the fertilizer and heavy mulching. Avocados grow year around, though they only flower in the beginning of the year. I was under watering and under fertilizing my trees. When I put on Osmocote Plus and doubled the water the leaf issues disappeared. Avocados are prone to boron deficiency (causes leaf holes) among other things, so a good fertilizer is essential. Your tree is plenty big to hold fruit, so if fruit is dropping, it's a water/fertilizer issue.

Your photograph shows evidence of persea mite infestation. I'd hold off on the fertilizing right now; excessive nitrogen can increase your damage.