I would generally do one circuit at a time ie lighting up or down and you probably will be putting more circuits in so you should be able to leave most still live. As for bonding if its not to much trouble good idea to do that as its got to be done any way. Every jobs different so play it by ear.Batty
That is the underlining point...
NO two jobs are the same...
i.e.
some properties it is easier to work circuit by circuit..
other times room by room due to needs to move furniture.
sometimes you need to use the old cables to pull new ones in.
Often cooker circuits (those with a 13a socket) are good ones to leave till last or do first cuz stand-alone radial can be left powered up and give you a power point to keep on for customer.
If existing circuits are radial, can be easy to keep just a few bits on while killing the rest off.
If it is a ring you could break the ring at an easy point & drop a lower rating fuse in the old board to keep a couple of sockets on as temp radial.
Wago's (or similar brands) are very good at doing temp power connections over night that you will diss again the following day.
Bonds?
it all depends on the cable routes?
Other factors include if you can fix new CU adjacent to old CU & swing circuits over one at a time...
Or if the whole CU needs to come out before you can stick your new one on!
HTH