You mean ElectrumX? It can run on my Pi. Is that what you mean? Doesn't it use Core as a data source?
No. Directly. ElectrumX depends on Core, but it is a separate server by itself.
It's not the storage constraints; I could unplug my external hard drive from Pi, plug it to my computer and use it there. The problem is that my computer does not remain open 24/7 while my Pi does. I need this mainly for the lightning network and generally I don't want from my node to ever go offline. Also, running a node from Pi does not use computer's resources that could make it go slower.
If running Bitcoin Core slows your computer down, then you probably have more problems to worry about
. VNC would probably be your only option though, so yeah.
I think "custom servers" is probably a better description for what ranochigo was trying to say... in that they use their own custom RPC interface that is incompatible with the Bitcoin Core RPC.
That is correct.
Then configure Bitcoin Core on your computer to use the blocks folder on the NFS share. Though, you may run into problems if this folder is being used by two different Bitcoin Core instances at the same time, so you could try mounting it read-only (and to be honest, I don't expect this to work either since you may not be able to make transactions, so perhaps making a simple GUI wrapper around bitcoin-cli is a better option).
Core needs to be able to be able to obtain a lock on the directory so you cannot possibly run it in the first place.