I would run PEX homeruns to each fixture, no joints buried in walls. PEX with sharkbites in easy to work with, far cheaper than copper and no one will steal it from your home. If it freezes it will be undamaged when thawed.....

the electric tankless sound like a good idea, but have major disadvantages.

I would run PEX with recurcliating lines, insulate with expanding foam, and keep the existing tanks...

even if you install tankless keep the existing tanks for easy reconversion