On the cusp of A-body ownership: Help me with a 1969 Valiant!

Welcome to the site, that's a nice car that you've got there.
I have a couple of '69 Valiants myself.
DO NOT disconnect the power steering and drive it! Can you say ''totally unsafe'' or ''liable'' if you get into an accident?
Mopar power steering systems are known for their light feel and twitchiness.
You can shim the relief valve on the steering pump to decrease the over assisted feeling that you have, just google Mopar Action Magazine and then go to the tech archive section and do a search. It's very easy.
Same place for a comprehensive set of articles on how to do a bbp disc brake swap properly. The article is called ''Disco-Tech''.
I like your idea to convert it to bbp front disc brakes, the stock 9'' brakes are terrible.
It should be easy to find Mopar wheels for it, they made millions of them. (Literally).
Don't cut up the radio delete plate to install a stereo, they are hard to find in good shape, and oh, the passenger side mirror isn't factory, that might be why it's giving you trouble.
I hope this helps.