Insulation and heating queries for renovation

[Gladewood]

Major renovation of our early 1990s built bungalow which includes side extension and attic conversion of which roof will be fully removed and more than likely replaced with truss roof.
Lots of questions regarding best insulation/ heating system etc..
Existing house is 80 sqm, hollow block walls on uninsulated concrete slab. Extending 35sqm to side and 2 rooms in attic. Gas central heating - old boiler!

Am considering removing concrete slab and going for underfloor heating with air to water system -
Q1. Looking for rough costings to remove slab/ and install floor insulation and under floor heating and air to water and likely money savings per year?
Q2. Or would new condensing gas boiler with radiators be more practical?

Hope to go airtight route as we will be stripping all inside walls - Q3. Looking for best system to airtight and insulate bare masonary walls on inside.

Also, very concerned about cold tiles and in turn cold feel to large kitchen dining room area if we don't go for underfloor
Q4. Looking for info on alternatives for taking the really cold feel from tiles.

Any help greatly appreciated!