cylinder spec

Hi,
Just bought house, 7 bedrooms, 280sqm/2800 sqft approx.
Copper cylinder needs to be replaced, I'm thinking 300l stainless triple coil unvented. 6 mains showers, want stove and oil boiler to feed in, and spare coil for solar in future. Is there anything else I should look for in cylinder, temp stats etc?

You cannot have an unvented hot water with solid fuel.
No uncontrollable heat source can be connected to unvented cylinders as this is against regs and is extremely dangerous.

I'm not saying you won't find somebody who will install it for you, but unvented cylinder certification is a separate training module and certificate.