You can fit a lot in a 4 cylinder pickup; just need to be strategic. Air bags will help it not sag. Just be mindful not to exceed the GVWR. I think @Deanswc has 4 cylinder Tacomas in his fleet, and he does a mix of power washing and window cleaning, as well.
Here’s my truck build. It’s a long read, and not all of it will apply to you. Feel free to skim a bit. I went with a flatbed, but there were some good suggestions made from people who recommended sticking with the stock bed and getting a slide-in skid to hold everything. Reels can go up on the bed side rails, vertical tank(s) can go up against the headache rack, etc.
