EPC D is average, and not bad for an older house. The current minimum for a rented property is E, with a proposal for that to go up to C by 2025 for new tenancies and 2028 for existing tenancies: something for you to be aware of if you were thinking of letting it in the future. You should be able to see a copy of the EPC assessment which will tell you whether there might be any further energy upgrades which would give a reasonable financial return.
(If the house has gas central heating then you might need to be aware that the UK getting to carbon neutral is going to need most gas boilers to be decommissioned at some point in the future. But given that this is currently the cheapest and most efficient way to heat a house that's on the gas grid - that's every property in a city or town, basically - this is going to be an issue for almost every property, and one the government is going to have to come up with an answer to, I think. An air source heat pump seems the most likely alternative at the moment.)
Underfloor heating is great: I've retrofitted it into my older house where practical. It's energy efficient, it's a nice feeling (like having an Aga under the floor, I think, although that's a rather British reference), and it definitely helps not to have radiators if space is tight.
New roofs on yours and the adjoining houses might be helpful: you'll still have to make sure the gutters don't get blocked by leaves to keep out damp.
I'd definitely want a full structural survey, although if the house looks nice and level and sturdy it quite probably is. There should be building regulations certificates for any structural work that's been done, which tells you that a surveyor from the local authority is happy with the standard of work.
UK housing stock is generally much older than in the rest of the world, partly because the land has been settled a long time, partly because we were first to the industrial revolution with its concomitant population increases and wealth for building and partly because we haven't had ground wars knocking it all down. The house my father grew up in was 500 years old and reputed to have Roman tile in the basement, the house my mother grew up in was only 300 or so years old. Very often the older houses have the better locations.