I started buying materials for my house back in 2010 and stock piled a lot of it.
But almost all of the electrical and plumbing I didn't do until 2020 as I wanted the most up to date Equipment I could get.
Yes parts are not cheap, but they are only slightly higher than the last build I did 2 years ago.
I also built a second copy of my house 2 years ago.
I buy everything from some great supply houses, that I don't pay anywhere near local costs for parts.
The pex is $233.59 for 1000ft you would need 2 rolls to do all of it perfectly.
$1475.00 in foam, yes that's the expensive part of it.
That's all you need to do now, you can do a boiler and all other parts later.
The boiler you would use is $1299.77 for 199,000 BTU.
You would be looking at about $600 in supporting parts.
I have three zones in my garage and it's 1080 SF, for 1500 SF you would want to do 4 zones.