This sounds like a good idea as people are struggling with the concept of a formal "contract", which does not always exist for a specific service. I guess you are suggesting a general document you have created that highlights site requirements and the importance of their service but can apply to many different providers? You then get them to sign off on that, also after reading some key procedures like hygiene etc?
As for which services, I always connect with anything "product related". While the painter can be related to the infrastructure/facilities prerequisite it is probably unnecessary to do so but definitely needed for pest control (easy as a contract is needed there) but also calibration, laundry provider etc...
I have a Contractors code of practice which is the general food safety/GMP that you would expect from anyone entering the process area,
I have had to customise the ones for specialized areas like pest control,and laundry to include the service expectations ( number of visits, what we require if there is an infestation, the colour coding of clean and dirty)
I print 2 copies, ask the provider to read them and then sign both, they keep one and I keep one on file. I review annually to make sure that we are all up to date, if there are any changes to be made , I make them and then spend a week or two chasing various contractors to get the document resigned ( that doesn't happen very often happily).
I have attached a generic document for anyone who wants an idea of where to start.
I try to keep documents to a minimum so I try to create documents that can tick as many boxes as possible.... Many of my docs have originated from this forum ( thanks to everyone whose work I have plagerised).