Schopenhauer. It's a no brainer then!
If you're adding value and staying longer term, it makes much more sense than ploughing money into a ready made place.
You can start small by doing one item/room at a time.
Plan and research. Look at starting with rewire replumbing and new central heating. Followed by plastering or dry lining any walls needing it.
Then look at new kitchen and bathrooms.
Do the loft last if you're a bit short of cash just now.
Or if you're able and can afford it then possibly borrow towards the loft conversion? If you're staying long term it makes sense.
It sounds like a really good project.
If you're finding yourself short of cash during the project look at perhaps ex display or second hand kitchens. Well worth considering. You could save a packet!
Price compare bathroom stuff on eBay before buying
And during January and June and August most bathroom and kitchen places have massive sales. 25% off. Really works well when you need tiles and flooring too.
And as someone else said, haggle where you can.
Bear in mind that the labour costs for doing the works to a good standard can't be minimised. If someone offers it too cheap then you may get awful quality and finishes.
Your savings are in materials and fittings you put in.
Good luck. Have fun with it.