Extension advice and pointers needed

[extensionhelpneeded]

We're starting a 2 storey extension next week. Builder is good to go, we have the finances in place.
Planning and building regs all agreed.

It's at the side of the house and there are 4 knock-through points so we know we will have to move out at some point. I work at home so,if it gets too noisy and disruptive I'll have to go work elsewhere. Fortunately we have friends and family nearby who can help out.

I'm quite anxious about it all. The work will take about 4 months and the builder assures me they are good at sticking to timeframes. I'm fully prepared for it not to be the case.

He also wants staged payments and the final 25% isn't paid until the job is complete and all snags dealt with.

So what I'd really like to know is, if you have undertaken a huge project like this, what you would have done differently, any useful tips, pitfalls that you fell into or avoided.

Don't get overly friendly!!!!
Cordial but professional is best in my experience.
Very unisual that a builder would leave such a large final payment until after snagging on such a large job.
Normally it's last major stage payment with a certain amount left on for snagging.
Good luck.

Follow pigletJohn's advice and get a cannister vac from screwfix. Nice builders bring their own. But you really can tidy up a lot with them.

Give the builders a key, be there in the morning when they arrive in case they need to talk things over with you but then go and work elsewhere for the rest of the day until after they have gone home (lots of builders start early but finish about 4). Try and get away from the house during the day as much as possible. That way they can get on with the work without you being in the way and you won't be as disturbed by noise etc.and won't have to make a round of tea each time you want one yourself!