ChiSau1
The way forward depends to some degree on whether
(1) you have enough dosh to buy it yourself, and are just looking for others to contribute towards the fixed costs
(2) you can afford to buy it but can't afford to keep it, so you need the others
(3) you cannot afford it at all yourself
Most groups you see around are (2) or (3). But with (1) and your question suggests that might be possible, you have better options. It looks like a certified aircraft, cost around £60k, and they normally come (new) with a Transport CofA so you can rent it out.
You can set up a ltd co., put the money into it as an interest-free loan (not forgetting to register a first charge in your favour at the same time) and get the company to buy the plane. Then you can rent it out to others, and you can pick and choose who can fly it.
The other option is a traditional syndicate where the plane is owned either by the partners directly, or by a ltd co. of which they are all shareholders. That way you get a lot less control but you don't need to put up the cash yourself.
A limited company is a lot better for the renting option because it looks more like a proper business and you've got a much better chance of being able to claim back VAT. Getting VAT back on £60k will pay for a lot of flying, but you can't do that in a partnership - you have to do rental and the renters have to be "arms length" people. You also need to pay for your private flying at the same rate as you charge it out at, to help avoid the benefit in kind issues.
In the end, the operation has to make enough money to recover the hourly costs, and recover enough on top to cover the fixed costs (annual, star annual, engine overhaul, insurance, hangarage etc), and this is the case no matter how it is structured!
Also a ltd co. should protect you from personal liability if someone else has an incident which is not covered, or not adequately covered, by the insurance. Whereas with a partnership, all partners are liable and there is total reliance on insurance. The reason why few people worry about this is that very very few GA incidents involve 3rd party damage. But passenger liability is real.
Just a few starting points to look at...
Justiciar
I think you will find the 5% min shareholding stipulation is only for Private CofA aircraft. A plane on a Transport CofA can have more than 20 partners in the group, or sub-5% shareholdings in a limited company that owns the plane. A Transport CofA permits unrestricted rental, to anybody for any purpose (subject to the renter having licenses/ratings/AOC/etc).