We recently viewed a similar sized period house (in London though) with our builder which looked to be in a worse state than this one and were looking at £500-600k including roof/new heating/plumbing/kitchen/utility/bathrooms/ceilings/plastering/windows etc etc. that was labour/building materials only - not the interior finishing like flooring/decoration/fireplaces/bathroom fixtures/kitchen etc (which on almost 4000 sqft is significant). We ended up not going for it as we could see costs spiralling. Hopefully Somerset would be cheaper than London, but materials prices are wild at the moment.
We've recently renovated our current house which needed a total refurb and is smaller than this. The renovation cost just for the interior of the existing house (4 bed, 1600 sqft) (stripping out/heating/plumbing/electrics/labour for 3 bathrooms and a large utility/plastering) was £100k. The roof was covered as part of a loft conversion but say £30k for a much smaller roof than the one you're looking at. Again no interior finishing included so tiling, flooring, decorating, fireplaces, bathroom fixtures, cornice etc etc was not included in that. Decoration for the whole house (ended up with about 2300-2400sqft) was £25k. We did 2 extensions (loft and double storey) and the total (including interiors but not garden) was £700-800k overall. That was pre-pandemic cost increases as well.
Do you have a trusted builder? If not I wouldn't risk it. If you do, take them to view it and get their opinion. But take any rough costs they give you with a pinch of salt. Our rough costs doubled - you just don't know what you'll find when you start stripping it all. You will need a sensible/large contingency. As others have said, given the location will you make your money back (even if not a profit)? If not then it's not worth it.