House extension brick n block and garage extension Diy TF

Joining the forum in the hope of finding the answers even before asking the questions and thus hoping to avoid any mistakes!

6x6m single storey rear extension, brick front & block sides (hidden by garage and boundary fence), 3.6m 3 panel glass bi folding doors, vaulted ceiling/roof with velux or two, about 20 degree pitch. PD build been applied and cleared then after thought was I'd add 3x5m to end of detached (but adjoined) garage, it;s brick & pebble dashed but doing the add on in self made timber frame. Doing some work myself though I'm no brickie so that will get outsourced as I don't want to look at it and shake my head every time I look. Poured footings two days ago using Volumetric lorry and line pump, Went 375mm off damp (allowing block and two bricks) on house and 185 off damp on garage (flat block & a brick) they are both 50's build and wont have DPM's. Have sewer running through so dug metre wide pits either side about metre deep (from ground) went below the pipe either side but not under it. We needed build over agreement (done online) and shuttered that off before pour. Next phase is pull off oversite and dig a soakaway and it's drainage runs before digger and dumper can leave site. Then block & brick up to damp, hardcore and blinding, knock a bit of old kitchen down and break out its old slab before pouring new slab all over. Going to do wet UFH in screed, so insulate on top of concrete slab then install it myself onto that (recommends for wet systems/suppliers welcomed) it's south facing and we work from home all day, could insulate under slab and install into concrete and omit screed part but if it goes wrong its a hard dig out of the concrete and being south facing I don't really need the heat retention of a slab as in Summer it's hot enough. The garage timber frame will be single skin build to specification which would pass regs if we later convert garage so have insulation in slab too and walls probably 150 studwork insulated within, osb clad and breathable sheet with battens and some form of weatherproof cladding, not timber.  (Any advice welcome on insulation and cladding) Think that sums up where I am.

Regards Mark