What are the dimensions of the screen? (Height and Width)

It 10” wide x 6.5” height. Diagonally across it is 11.5”

Is the display height adjustable? I have a panel not far below my radio slot din that will block some low hanging displays.

Yes. It moves up and down approximately 4".

Can I connect the factory rear camera? Tacoma 2019

The head unit uses an RCA feed and an auxiliary wire to initiate the back up camera (powered through the reverse light usually) - you may need an interface adapter from your Tacoma to the head unit.

Where is the USB ports

There are two short USB cables on the back of the radio, one for Apple Car Play/Android Auto and one for USB charging/Media input. You will have to extend those to reach the driver/passenger compartment. Where and how you route those is dependent upon the vehicle. I used an extra charging cable for my phone for the Apple Car Play/Android Auto but you will have to buy an extender cable for the USB charging/Media input. Bad design for an otherwise great radio. I love the large screen which makes the menu and icons easy to see and touch while driving.