van mount is def best BUT for now as you are just starting out with it i would get a cheap bpack from john hewitt eg esr 16, dont wear it on your back tho - nightmare. has a good handle to just carry it round and just put a length of hose on it.
then when you have got the hang of it and customers are happy with it then go for the van mount, that way the bpack just becomes a hany tool if the hoses from van are a pain for certain jobs ....