I have a similar-sized guest house/B&B. I use standard domestic indirect hot water cylinders (x 6) working in pairs, with large cold water header tanks (x 4) in the attic. I found it best to zone my central heating and so have 6 zones, two on each floor of a 3 storey building. The property is heated by 3 x LPG boilers (2 smaller models ~Myson Economists working side by side and one larger one ~Ideal Concord which, on its own will heat half the property). These boilers do heat water for the shower/bathrooms (x12), but the cylinders also have immersion heaters which, though expensive, are cheaper to run (where possible using Economy 7 and Evening and Weekend tariff) than LPG. I also have a solid fuel Aga, which helps with the hot water for 2 of the cylinders and a large Coalbrookdale Darby, a multifuel stove, in the residents' lounge which is lit every winter evening and burns logs and coal mix. This stove, which the residents love, is connected to the central heating system via a H2 panel, which is an excellent way of safely linking up boilers of different types and also helps heat 2 of the cylinders. Once it reaches temperature, the 2 Myson boilers click out and the stove maintains heat, with the boilers clicking in and out as necessary.
Hope this helps.
BruceK
Hope this helps.
BruceK