I’ve also struggled with the ‘contemporary’ designs of most front doors that have modern construction meeting insulation and security requirements.
I’ve ended up going with a Hoorman which is quite uninspiring, but was able to match the garage and personnel door that sat alongside. RK offer flexibility to bespoke many elements and could have improved on my chosen aesthetic, but not substantially and at an approx 80% uplift in price. If it’s exclusively the front door and you’re not trying to align the design with garage I think RK are a good starting point. Www.urbanfront.com is good for inspiration but you’ll need some quids to go shopping there!
As you know Mike I am doing similar. I've gone for blowerproof on all floor to wall joins, wall to ceiling, wall to wall, all blockwork mortar so very little left of the blockwork is visible.
All back box interiors are taped, encased in plasterboard adhesive. Plasterboard adhesive on all board perimeters. Upstairs ceilings are all double boarded, first original ceiling is sealed to wall with blowerproof first ,before hand gaps filled with flexible expanding foam and tescon tape above it in the loft.
All cable penetrations, foamed if existing and sealed from below if accessible. New cables are put in conduit and using Stoppas to seal them, these are good but don't hold up to well when moving cables for new lights from below and need refitting (get pushed off of the conduit) which is a pain when it comes to the insulation in the loft.
It's been going on since April last year and still got 5 rooms to sort and not managed to switch on the mvhr yet as too worried as not all the ducting is covered in insulation (this week hopefully it will be sufficiently covered)
Don't forget to make sure insulated cavity closers are used on door and window openings, not just fitted but sealed with no air leaks whatsoever. We fitted or i should say the builder with a bit of my help fitted them using expanding foam + CT1 or sticks like **** adhesive. Made a difference around our windows that's for sure. Make sure no holes are in the lintels too.
For me it's been a massive learning experience and I wish I was less caring and just turn up the heat as the cost has been huge but we like where we live and plan to be here a while.
Looks like the substation is on the plot and might mess up your frontage a bit? If the asking price is 'building plot' price, then it needs to have at least outline pp for a dwelling. If it hasn't got pp, then it's a bit of waste ground and should be priced as such. Any premium paid over that should be subject to the grant of pp as @ProDave said.