First post here.

What I think is a simple question, probably not unusual.

House built in the 1950s. Over the years, various owners have added to the electrical system. But the mains are plenty for the home.

My problem is that there are a few breakers which have more than one wire attached to them. I understand that this is a no-no. We have only lived here for two years, but we plan to move in a couple of years and I suspect that this wiring will not pass a home inspection (though it passed just fine when we bought the place!).

I want to correct the probem. Obvious answer seems to me to be a sub-panel. I want to do it correctly and safely.

Can I put a breaker in the main panel to supply the sub-panel, and run a heavy gauge 4 wire feed to that sub-panel, and keep it located close to the main panel?

Do I have to have a splice box, or can I splice the extra circuit feeds inside the mains panel? I am assuming that the wire on the circuits that I need to split out to a sub-panel will not be long enough to reach a sub-panel.

Are there size requirements for such a box, and are the splices required to be a certain type of connection, or may I just use wirenuts?

Do I need to isolate the neutral bar, to avoid 2 paths to ground?

I have a lot of experience with wire and voltage, I've been a stagehand all my life working with movies, theater, and concert power and the various voltages and connectors involved. But I am totally out of my element when it comes to homes and home wiring, beyond adding an outlet or ceiling fan, or changing a light fixture.

Thanks in advance for any help and advice,