Just so you know, if you order from the Ford accessory site you can get the parts installed for $210. So you would be looking at ~$550 + tax for parts and labor.
https://accessories.ford.com/products/ranger-2019-2021-trailer-brake-control-towing-pack-3
The mirror covers for the Lariat are different than an XLT. The Lariat has cutouts for turn signal lights. They will not work on the XLT. Also, I don’t think Ford commonly sells pre-painted parts. Most are sold “ready to paint”
XLT Cover Part number 5
Lariat Cover Part number 7
I have a factory wiring harness for a truck with the rear parking sensors and the 7 pin receptacle that would complement your install if your interested.
I would just wait a day or two before washing. If you use a power washer at home don’t get too close to the stripes. Coin-op wash pressure should not be a problem.