Dear Canard It seems you have been through a thorough process of choosing this builder and co. With regards to timings, it is very difficult as it depends upon the artisan(s) concerned (he/they has/have his/their own reputation to think of) and what his/their planning is like re. future projects (in terms of leaving site to start another job). Ensuring that the payment of monies is stacked in your favour could help maintain their 'focus' on your project, ie ensuring milestones are agreed and reached before payments. Artisans do qoute payment schedules on devis' with timeframes, but these are negotiable, especially on such a project. One note of caution, the Mairie provides a list of local artisans. Check they are insured (carrying the decenal/10 year insurance) to do the works each artisan is qouting for. Always ensure you have seen what you need to see, do not rely upon anyone else and feel that is ok then as they must have checked. I was told a story only yesterday of a French Architect who wasn't actually an architect and had fabricated it all. One couple took 6 and a half years to sue, but did win and now others are coming out of the woodwork to sue him! As you have said it yourself, it can go horribly wrong, so triple check. Good luck with the project.