If you read enough build threads here you will pick up all sorts of good information.
There are plenty of "Next time I am going to do "x" different" comments scattered about. There are also plenty of good & successful ideas.
My biggest gripes on my last conversion (Eagle 10 not Skoolie):
Floor: I covered the access panels for the shifter, clutch and throttle linkage. I was told by a very sharp bus converter that it would be ok as we had converted to auto trans and would never need to access.
After a few years it got to where I had to brace myself in the drivers seat to get enough leverage to press the throttle to the floor. I finally abandoned the mechanical linkage and in$talled an air throttle.
Windows: I put in lots of windows. I wanted open and airy. Worked great in mild weather. As soon as I hit hot weather I wound up making insulation inserts for half of the windows. When I hit cold weather I made insulation inserts for the other half. Too many windows.
Also, I installed single pane windows. Never again. Double pane all the way.
Toilet & black water: I installed a porcelain RV toilet and an 86 gallon black tank. Every other RV I have ever owned had a 15-30 gallon black tank. Having plenty of capacity gave us great flexibility and the ability to dry camp for extended periods.
We did that right but next time it will be a composting toilet. No more black tank.
Drivers A/C: I removed the over the road A/C. It did not work. I thought that if I needed A/C while driving I could run the generator and the roof air. That worked great for the passengers but the poor guy up in the fishbowl with the sun blasting him didn't get much benefit.
Next bus will have some kind of drivers A/C. Either engine driven or ducted from a roof air that puts plenty of cool air directly on the driver.
Selling: I sold my bus a few years ago. Probably my biggest mistake in the whole process....
You have found a GREAT resource for conversion information here. There are plenty of folks here who have walked the walk and can show you the end result.
Read, read, read and then read some more