That is a nice little trailer.
You asked what I would do differently?
1. Larger supply lines to the pumps. I am a believer that a large supply line reduces the frequency of seal replacement in pumps. Ours are abused to the extreme, and we have rebuilt more engines than pumps. I think there is usually an engine in our shop for rebuild, at least once a week, it seems. I hate Briggs motors, just because of that. I am fortunate that I have my own mechanic.
2. I would not have the 90's on the machine supply. They restrict flow.
3. Larger feed hose. At least 3/4 inch per machine, especially at that volume. If you can locate and afford 1" even better.
4. You need a a brace across the hose reels, because they are likely to wobble and break.
5. Lighting and cones. I would put a little LED strobe on the back, and get some bigger cones, with reflective collars. The reflective collar make them more visible in the day time, too.
6. It looks like there might be enough room for a roof cleaning pump. The tank could be problematic, unless you were to downstream the love.
But really, I would give your trailer a 9 out of 10. The last thing is, that it is just too clean. Lets get it to work making money.