I would love to be able to give you some advice Stef on big contracts but alas my knowledge is limited in that area for tiling. However, in a previous life I was dealing with contracts from as small as £500, right up to 300k. What I will say is make sure that you are watertight as they say because the customer i.e. who you are are working for will look for any small detail to hold back/not pay you at all. It's a massive step to move onto a contract of this size. I'm sure you have the bottle to go ahead with it and I'm sure you will project manage it well. It's knowing what to do and how to approach and handle things if they go wrong. But the same has been said, nobody ever moved forward by standing still. Good luck on this one.