Hello, I'm just trying to design a system for a new house, doing refurb now so have a few weeks to finalise design, and am stuck in a few places. Wasn't sure which section to post in, hope this is OK.
Sketch of system as follows:

Some parts are a little unconventional but reasons are:
- Designed so that if lazy (or new owners in future don't like it) can use Combi including DHW as normal boiler (will have swap over valves in airing cupboard to use combi HW instead of cylinder).
- Will use eVolution 26 with SCWS as sealed system + in Smoke Control zone.
- Vented HW cylinder so it can be pumped for (high) power shower.
- Small buffer store to be used ad hoc for in the mornings to heat a couple of radiators for a short while without having to light WBS. Radiator TRVs will probably be LightwaveRF. Not a combined TS with DHW for previous point reason, plus don't want to accidentally use hot water with the heating.
Significant control features are:
- WBS pump P1 controlled by flue stat T2 only
- Radiators zone pump Z1P controlled by T1 stat only (at quite a low temp), no timer or room stats
- TRVs will be LightwaveRF (individually time programmable)
- Tune the combi's return stat so that when its timer/room stat calling for heat but WBS is burning and keeping up, it will just circulate without firing.
So the bits I'm struggling with are:
1) How would I "charge" the buffer store at night when I know there will be no time in the morning to light the fire? The only thoughts so far are to use a LightwaveRF relay in series with T3 to energise the pump ZP3. Or a switch in the airing cupboard!
2) Similarly, how would I use the heat in the morning. Again, lightwaveRF relay my only idea so far.
3) How would I go about sizing the buffer store? It would be needed for maybe 20 mins of heat to radiators in bathroom (heat leak) and kitchen (others to be shut in with the TRVs) - sizes unknown as yet, but any rough and ready calculators?
4) From what I understand, it is only possible to connect 2 heat sources to a Systemlink manifold - their documentation states that for a 3rd source, two would have to be linked together with a pump, but no more info than that. Any ideas on this, or an alternative way perhaps to piggy back the buffer store on the combi flow/returns?
5) Solar thermal heat dump for hot days - I'm planning to use the spare relay on Delatasol ES and stat T4 to circulate pump Z2P when getting too hot. Being a neutral point manifold I guess it will just circulate around the coil loop, but be enough to heat the whole manifold to reach T1 setpoint, which will energise Z1P and lose heat around the radiators. Does that sound like it will work?
6) The SystemLex instructions refers to using the spare relays to enable Hot Water Priority, but not much more. Anyone with experience of that?
7) I will be handling a lot of the plumbing, but will need someone with wet HETAS for WBS installation and appropriate qualifications for the key parts and signing off the rest of the install for building regs. Am in Nottinghamshire - any recommendations?
Hopefully that's vaguely clear, many thanks in advance for any advice.