You could do a decent amount for 100k but I think you’d be looking at renovating what’s there rather than the plans- so no moving walls or knocking things down.
I’d be forgetting about the finish and thinking about whether it’s dry, warm, mould free and safe. It looks like it has some radiators (good), wiring doesn’t look immediately dodge (good) but there’s also evidence of damp and I bet that extension is single skinned (no insulation). So if you offer get a good survey which looks at gutters, roof, boiler/ heating, plumbing, electrics. And windows, if the windows all need replacing (especially those new ones), that in itself could cost 30k easily.
You can bring a nice kitchen in for less than 20k and you can often get kitchens and bathrooms on interest free credit for a year or so but that will depend on your ability to pay it back too (are you working or retired?).
Also bear in mind that kind of place will have ongoing costs- there will always be something to do. That said it’s definitely also hit huge potential for an Airbnb or holiday let if you needed to generate an income.