building in wexford

We are about to start restoring an old 2 up 2 down cottage with a flat roof extension to the side (which houses the current kitchen and bathroom). We have permission for an extension of 800 sq ft to the back of the original cottage. THe original cottage will remain and we are looking for advice on how to insulate... If possible we would like to expose the stone walls, we are knocking the internal wall as the two small rooms are just too tight to be functional. The ground floor of original cottage will be the sitting room and the new block the hall, stairs and kitchen/dining. Any suggestions about heating also.. considering solar for hot water and some heating, can't afford geothermal, what about HRV (heat recovery ventilation). We will definitely put in at least one solid fuel stove. Any suggestions gratefully accepted. Cheerio.

Also need recomendation for someone to fence the site with stud fencing ??
Would like to put in sash windows, Can't believe we are doing this but considering pvc (on basis of low maintainence) any advices or suppliers recommended?: