Hi Nick, et bienvenue sur le forum.

Having exhausted my minimal French, let's get on to a safer subject

The 345W is as you know wood only - or similar CV fuels such as lignite or peat, designed to burn on an ash bed. It's a derivative of the 355, on the 300 chassis, formerly known as Supreme then Nouvelle. It has the same firebox (is basically the same cooker) except for the riddling grate. Cynics say Rayburn, ever the opportunists, only changed that because they could offer 5% VAT. If you have a great supply of wood, this is fine. If not, the multifuel 355 may be a safer bet.

Alternatively, as per a recent thread on here, there are other cookers, some French, worth a look. Rosieres, Franco-Belge, De Dietrich etc. Or Wamsler, Windhager and their ilk.

As far as installation goes, a vented thermal store (TS) with DHW coil is fine. You don't say whether this will feed rads, or if they will be direct from Rayburn? That decision will affect the sizing. Aim for 500 litre plus if you want to be able to store some of the wood-produced heat for next morning's shower and rads etc. Specify one with a solar coil and a few extra tappings if poss, so you can use solar (or other devices) in the future to reduce the log demand.

Use the injector T as it has a proven history. Fit in the return near the boiler, with high and low pipe stats wired to bring the pump on when temperatures rise.

Heatleak aka gravity rad on thermosyphon is more involved with a TS. Yes, you can take it direct off the Rayburn, but then, unless you include an electric element, only the Rayburn can heat it. The alternative is to take a heatleak off the TS itself, meaning you can use your heatleak on sunshine or W.H.Y. too!

Hope that helps as a preliminary.

Ed: Calorific Value. Sorry! Used it to differentiate it from the solid fuels Rayburn usually recommend on their solid fuel cookers.