Upgrading existing solar system in place?

Currently i have a ~5kW solar edge inverter/solar array that was professionally installed at my house (i fully own it).

I would like to upgrade this inverter to an 18kW EG4 unit and add an additional ~8kW of solar to my recently added back patio cover roof. The existing 5kW array does have "optimizers" but i should be able to feed the 2 strings into 2 of the 4 MPPT solar inputs of the EG4 18kW, with the new 8kW array going into the third since all those panels will be in the same orientation, and leave the 4th open for a future shed i might add in the future with an additional ~8kW array.

Since my home is already set up for net metering, this should be a fairly simple upgrade in place? The only change i might make is moving the inverter to inside my garage which is temperature controlled for when i eventually add some battery storage. I would also add a critical loads panel where i would move some of the circuits from my main breaker box. But i know i'll still need to keep a solar disconnect switch on the exterior wall. But the EG4 18kW inverter should be able to fully support a grid connection that won't back feed but also keep the critical loads panel operational during a power outage when battery storage is there.

Just trying to gauge how DIY-able this is without having to jump through a million hoops of permits. I am not an electrician, but i am an electrical engineer and no stranger to DIY home electrical projects. Thanks for any suggestions.