We used to pair contracts with contract values. But these days we tend to work more on the basis of the number of subcontracts, or the amount of work being undertaken by a subcontractor relative to the work of a main contractor. Under your chosen contract, what powers do you have to seek redress from the sub-contractor in the event that the main contractor goes bust? Wherever there's any degree of complexity, I would tend to favour a minor works contract over a domestic one. Whatever you choose, make sure that the rectification period is for one year. Six months is a poor choice, because those six months might be in the summer - when there's not much wind, snow, or rain.
Also, I would be extremely wary of agreeing your own terms. Our clients love to do this all the time. I think it's almost pointless, and inevitably adds more cost to the project. Stick to the standard forms. They've been written by a group of individuals/organisations from all sides of the construction process, so are intended to be as fair as possible/appropriate to both parties to the contract. Mess about with them at your peril.