Convert gravity system, pumped CH, add pumped DHW?

[wings1]

Hello,
I recently bought a 1930's house, have recently had fun (honestly I enjoyed this! ) working out I have a pumped CH & gravity DHW system. What I would like to do is leave as much existing pipework as possible and add a pump to the DHW circuit to improve heat up time and efficiency etc?

I guess the DHW pump should be smaller than the CH pump and I'll require 2 x 2-port valves for zoning?
Can anyone please advise how I calculate size of pump required, location for fitting in the primary flow DHW circuit and comment on any other additions required to the system?

Having two pumps, I imagine that I can just have each controlled by programmer for the CH or DHW?
I've heard there can be feedback on the pumps, so plan on fitting a relay on each pump, but not sure if particular type is required?

Is it reasonable to ask an appropriate person to wire up the system after additions are made to the wet system?
Would this be any Corgi registered person or does it specifically have to be a heating technician etc?

Apologies for long post, but so many people ask for additional info on other posts, which I'm trying to avoid!

Thanks a lot for any advice you can offer to this enthusiastic DIYer.

 

[spacethegas]

the system must be converted to fully pumped.
this would involve just one pump and the addition of a diverter or zone valves, cylinder stat, room stat, programmer & a minimum of trvs in all bedrooms.