you don't sound like you have the kind of setup where you'll benefit from going the DIY route, were you a one man outfit that might be different, but you can spend an awful lot of money that you don't need to spend if you are not careful!
I'd only consider goingthe route of the big boys (Ionics for instance) were I considering leasing a couple of systems, I understand that it can work out cost effective if you are equipping a couple of vans with a full system, it allows you budget and plan ahead effectively.
but a big fancy system won't do any better a job than a more simple system, ultimately it is still a brush on a stick (as squeaky might say)
As Alex has said, a tank and a delivery system + relavent poles & brushes in your van/s And a static pure water production setup and transfer pump at your base.
Whether you are commercial or domestic, WFP is fine for either, but the size of system you go for will be dictated by your work.
Take your time, check out the options but don't spend more than you need too!!!
Ian