The hives are going to be positioned in the centre of the farm once situated if I want to move them I'll
Have to remove for three weeks and then bring them back , they will be very close to both field beans, orchard and osr , I was thinking to keep them all together as to help with inspections .
The closer they are to these sources of forage the better I thought?
if it were me (and there are many ways of doing this), I would not have a single apiary in the centre.
I would have 3-4 apiaries of 6-10 hives near the perimeters and see where you go from there.
If the farmer is paying you to spot pollinate the crops, there are a number of published figures that can help with optimum pollination density's, but these are more for when you can move the majority of bees away to other pastures.
Sitting as close to the crops as possible means you NEED to lock the bees in when spraying. If a few hundred yards away, it becomes an option.
The first reason I would have multiple apiarys is to spread the bees to forage outside the farm without flying over it (efficiency), but also reduces the focus of bees from one spot. The farmer may want bees, but a lot of hives in a small area, can create a huge amount of flying bees in a small area which can be unnerving for some.
Smaller apiaries also give a degree of separation. diseases can jump from apiary to apiary, but if there is separation between them, it prevents bees drifting in a small area and lessons the effects. CCD is a good example. I have lost most of a 10 hive apiary to CCD, but those apiary's 1/2 mile away have remained unaffected.
You are right to think about other sources. Farms with few crops have boom and bust in foraging. A balanced area with hedgerows, trees and wildflower helps balance things out which will require less feeding during tight times.
Hard work - yes it is. But you can be smart about it to lesson the load. Your optimum hives will generally be as many as you can do at peak time. A large amount of hives swarming is really bad politics.
For a full time job, you would need many sites. Until you learn how to manage large number of hives, stay within the 40 BBKA limit to keep your 'insurance'. BFA membership requires commitment.
IMHO you should avoid sitting in the no-mans land between too big for BBKA and to small for BFA.
Just my 2 cents...