Re: Independent differently-configured instances running concurrently

[Javier]

> Note I'm a bit of a *nix noob, so feedback on the bash scripting
> side would be most welcome, in addition to anything emacs-specific.

I would define bash functions in ~/.bashrc instead of using several
scripts, just to keep all configs inside a single file.

#include in ~/.bashrc
emacs-vanilla()
{
export HOME=$HOME/emacs/homes/vanilla
export PATH="~/.cask/bin:$PATH"
/usr/bin/emacs -title vanilla
}

emacs-...()
{
...
}

> the different instances "stepping" on each other, either in RAM or
> perhaps writing back to global init configs?

That shouldn't be a problem unless you want to use emacsclient/emacs --daemon

> Any other comments welcome

For other environment variables you can check M-x Info-goto-node 
(emacs) General Variables