Handy Plumbing has been established for 10 years and have seen an increase in customers year after year.
If there is not much pipe work to do then it could be done in a day at a push but more two days would be a good amount time to install everything and get it all sealed up and good to go .
Personalty i very rarely take deposits this is because 90% of the time my customers only pay me for labour so i never ask for one i find this also creates a better relationship and trust from the customer . you will find a lot of the bigger companies will ask for deposits and then you will find some of the smaller tradesmen will as well but i would only expect to pay between 10-20% of the total amount personally i wouldn't feel comfortable paying anyone more then that before i saw any work being done.
Regardless of the regulations on new builds it is the plumbers job to know if what he is installing is going to be enough to do the job in hand and to keep the customer informed along the way of the install . this is how i work and if it is not doing the job properly then your plumber should have known or at very least after the system had been tested informed you that it needed them installed .
Could be a 3port valve letting by