New extension

The dear old planning officer has finally given me permission for my extension.
I'm building an attached single garage, utility area, bog and storage room.
The build will also include an update to my house heating system. I'll be removing the existing boiler and hot water tank and installing a new system. I quite like the Potterton Powermax HE - . Has anyone any experience of these?
To save space I'm also thinking of installing underfloor heating in the new utility area and bog plus through into my existing kitchen (existing concrete floor) and removing the existing kitchen radiator too. The only feasible system is electric and I'll be tiling over throughout. I quite like the look of the Penguin system. Again, any comments?
I'm starting with my spade in January and the project should be complete in 8 weeks. The final job will be a replacement driveway as the existing will be knackered by then. It's a total of 55sq m and I don't know if I should have PIC or blocks. Any comments here would be appreciated too.
I've done lots of re-furbs but this is the first time I've built anything from scratch. I'll employ a builder to erect the basic shell, roof etc and do the rest myself.
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