Just realised why so many tradders are put off by starting wfp ! The technological know how is very difficult to grasp with so many differing viewpoints !
It takes quite a bit of homework to appreciate the science of producing pure water and the economics of using the most cost effective methods.
The positive thing about starting wfp is I am having to really use my brain( which I never did at school ) and I know I will work safer and prolong my working life,
I am near to a mental breakdown with all the calculations but I think I will get there 
Yes I found things quite a struggle at first too. A few things went wrong that were unforeseeable (such as gearbox failure, small fire in back of van, pump breaking, and being let down on a place to do the filtering). So it was a baptism of fire. Of course a broken pump is no big deal now. Just keep a spare handy in case of problems.
It will come together. A few weeks/months and you will look back and laugh at your current worries. Just gradually build a small stock of spare bits (blade fuses, hozelock or rectus fittings, those little sleeves to mend wire breaks, pole hose, o-rings) and carry some small tools (spanners/screwdrivers, ciggie lighter (for heating hose), scissors) with you in case you have to fix anything. It's impossible to give a comprehensive list here but the above would give you a start. Everyone works a bit differently so the list for one person will be different from someone else's.