I decided not to bother stripping the paint, thanks anyway Hedge. I might still buy one of those Bahco paint scrapers though for future use as it's got 5/5 stars on over a 1000 reviews.
However, I've spent the last couple of days prepping the masonry. I washed it all down to get grime and cobwebs off and sanded the whole lot with 80 grit. No sanding machine, did it manually using a rubber sanding pad to put the sandpaper over. I've pulled away any flaking paint and sanded over that to smooth the edges. Even while it was raining today! I've bought a box of Touprelith F to fill cracks and I've scored the cracks with my filler knife to make it easier to fill.
I bought a tube of exterior caulk today and have just sealed the bottom of some of the window frames where they meet the horizontal sills and around the base of the verticals, because I had noticed narrow gaps. I'm not very good at it yet, I got a lot of excess sealant on the frames and the sills, so spent a lot of time wiping it away with kitchen roll and getting it all over my hands.
There's still some more bits to seal.
Tomorrow, if it's not raining, I plan to use the Touprelith and then I'm looking forward to painting it all with Sandtex white. I'm wondering if I can fill the shallow patches where paint had flaked off, but I don't know yet how thin the Touprelith will spread.