Best boiler - Condensing (not combi) - unvented......some questions...?

So far, my house has 3 zones. Tomorrow it will have another. In five years, I expect it to have up to 6. All heating zones have programmable thermostats. (Nice looking low profile Sunvic ones).
(Existing) 1. Downstairs CH radiators 2. Upstairs CH radiators 3. Heat bank (domestic hot water only) (Imminent) 4. Kitchen fan convector (Future) 5. Conservatory fan convector 6. Loft conversion CH radiators.
The locations of the valves do not have to be in the same place. The boiler and the heat bank are in the loft. The hot water zone valve (3) is there and the loft conversion zone (6) would follow. Unzoned trunk pipe goes down two floors into the understairs cupboard where the radiator zone valves are to be found (1+2). There is also an automatic bypass fitted here. The unzoned trunk then continues into the kitchen, round the back of the fireplace and under the units where kitchen zone valve (4) is already to be found, disconnected. Valve (5) will probably join it in the not too distant future, with the final leg in 15mm to the conservatory convector. The entire trunk line is run in 22mm. Each circuit drops to 15mm straight after the zone valve (except heat bank, which has a 22mm rapid recovery coil).
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