You need nothing, except to keep the grass maintained and (highly recommended) have third party liability insurance.
You don't need to restrict your usage to 28 days* and you don't need planning permission. If you go for permission, you'll be unlikely to get it, you'll draw attention to it and create yourself a load of grief. After 10 years continued use, you'll be pretty much sorted as long as you don't suddenly then start ramping activities up.
I see it so often where people establish a strip and then mess it up for themselves by inviting all their mates to fly in. You need to use it on a subtle basis and using a "take off and f**k off" attitude. No circuits, a quiet and high arrival overhead with a glide approach, and making sure you avoid bringing yourself any attention.
It's easy to do, but it's also easy to get it very wrong.
PS You don't need to win the lottery either. If you go about it the right way, you can speak with a farmer and negotiate an annual rent on 3 acres (500 x 20m plus parking area).
* IF you get a knock on the door by the Planning chaps, you will mostly likely have a 28 day restriction imposed on you. Prior to that knock, you can legally use it for 365 days per annum. So, the key is to use it subtly and sensibly.
I hope that helps.
ps
A lot of your likelihood of success with approaching the landowner is your attitude and how you go about it.
If you turn up in a polished white Audi and say, "Hello, I own an aircraft and I'd like to rent some land from you to fly from", you'd be better off not wasting the diesel going to see him.
If however you take the time to understand a bit about farming and have answers to the kind of questions he/she will ask, you'll be in a better place. You'll also need to take him/her for a fly so they can see the aircraft. Most non-flyers will assume it's a big noisy twin. It's just the way it is.
pps
And when you get to know him better, you can drop in and take him a cup of tea and fish and chips!!
