Marc ,
Getting your thinking cap on ahead of the wave and thinking of problems and the answers is the way round things most times .
I've often found that with your planning applications , if you can list twenty or so problems and item by item give the correct beneficial answer you're a long way to getting your permission.
I use Edward De BONO's , " Six hat method of thinking " to develop myself in to looking at life & events etc . from six different angles .. It's a brilliant way of exploring & developing projects and life in general .
I'd see if the county & adjacent counties has any similar applications and applications for temporary occupied cabins etc. in the countryside sort of thing , over the last seven or eight years and see how they went.
(Most now run this data on their websites )
For anything that were the causes for objections or refusals find at least two model answers you will do to prevent them happening and state them in your application.
Knowing how green some of the planners are, I suggest it would also be a sensible thing , to do an access and all types of waste management planning part for the application . I also included a nominated veterinary over watch & regular health visits to our small mammal farm .
I also added a fair bit about energy conservation and energy needs
Traffic , vehicular access , visibility splays and all different types of noise were also things I develop and gave model applicable answers for
You could do a whole health and safety section paragraph by paragraph with all the right answers .
In fact I 'd say do everything positive and never state the negatives ,doing the positives and and including your considerations for them and the answers to the considerations shows that your not just somebody hoping to build a house by the lake causing an intrusion into the open countryside .

Finding financial positives for the local area is also helpful , especially if you state that you hope to expand and take on employee's. Perhaps even to the level of running recognized training courses.
I'd also start looking at & talking with as many Councillors as youn can who sit on planning committees and ask them what sort of thing helps in getting permission . (
I'd also never ask any of them what causes them to fail nor would I get into arguments

with them .)
Before we did any of this stuff both my lass & I went on an EU funded small business development course where we learnt how basic outline plan , how to gain planning consent , construct the business , set up the office , tax & VAT and forecast financially .
To plan for the development of the business for several years ahead with a reasonable logical sense , hope & accuracy ahead .
Getting every thing from the course down on paper ( 37 sheets if I remember correctly) and having it looked at by a team of financial experts seconded tot he programme saw us get pound for pound matched funding from the EU under the economic development plan ( At the time this was called Option 5 B ) in high unemployment areas .
We also sought and got a lot of written & verbal support from businesses owners and farmers in local the area once we'd talked them through our plans and application
Three or so copies of the the whole business plan were also attached to the planning application . By the time it was submitted we'd come to know many of the planers and Councillors in a friendly helpful way .
To get to this stage we sought help from the local business enterprise trust ( BET ) and our local banks business section bank manager .
We gave our lady bank manager a simple positive overview of what we hoped to do and also gave a simple forecast of how we'd earn the money then asked her for help & advice in developing it .
Our bank manager knew exactly where to send us for this course and for that we are very grateful it must have saved us thousands & thousands of lost hours , dead ends and even more thousands of pounds of money .