Separate engine and pump matching resource / guide?

Greetings, I’ve searched through the forum and haven’t been able to find an answer to what I’ve been searching for, some sort of reference for building your own pressure washer rig from separate components yourself, matching engines with pumps in various configurations.

I’m starting my business as a side hustle at first, just picked up a small lightweight aluminum 4.5x8 trailer as my platform (limitations on tow vehicle). I’m targeting residential work in a fairly affluent area, and in order to keep size and weight down, I’m hoping to build a gear driven 5-6 GPM/3000-ish PSI wash rig, with at most a 50-55 gal buffer tank. (At this point I’m not planning a softwash system initially, and will likely go with an X-jet, so I’ll have batch mixing considerations, but will consider it in the future)

I’m looking to keep as small a footprint as possible, and looking at these small skids that are basically the size of a pallet, made to go into the back of small pickups, as my inspiration for build out of the system.

Where can I find this kind of information? From what I’ve read so far, I’m considering a Honda GX or iGX 390 as the powerplant, but really don’t know how to even search for applicable gear drives and pumps to build it out? Is this just a matter of calling up suppliers and seeing what the have or recommend?

Thanks in advance, and if I just couldn’t find this answered elsewhere in this forum, links are welcome.