Your watering schedule and how much to water really depends on your soil, the size of your tree and the time of year it is. During cold weather in Winter, especially if we get rains, I may not water my in ground trees for 1-2 months. Also as the canopy gets larger, there is more leaf surface area so you need more water compared to a small sapling.
Your tree doesn’t look very big from the few pictures you posted. I would recommend removing the blooms so that your tree can grow a bit larger.
Since your tree is blooming already, I recommend grafting it with a named cultivar. The Manilla mango seedling Fruit are not very good quality in my opinion. I’ve tasted fruit from many different Manilla Mango seedlings and I’ve only had one that was just ok with some fiber, nothing I would really buy at the supermarkets.
Many people think they are planting the “Manilla” like the the Ataulfo/Champagne/Manilla from the supermarkets but the Manilla seedlings from HD and many of the other nurseries are just seedlings and the fruit tastes very different than the Manillas you buy at the supermarkets.
The seedling Manilla Mangos often get Powdery Mildew on their blooms but once they get established, they still seem to produce fruit even if the PM were left unchecked.
Lemon Zest is one of my all time favorite Mangos to eat but it gets a lot of Powdery Mildew on its blooms. It seems to fruit better when grafted onto Manilla rootstock but this is just from observation off my tree.
Sweet Tart and CAC/COC would be good varieties to graft onto your tree. They are fairly disease resistant and set good crops in SoCal.
Simon