Changing from Roth IRA to Traditional IRA due to salary increase?

I have been putting money into a Roth IRA account for a few years, but now my salary is completely over the annual limit that allows me to use a Roth IRA, so I must use a traditional IRA. Do I need to open a separate account for my traditional IRA? I have Ameritrade, if that matters.

Should I roll over any money from the Roth to the traditional? (I would think not because the Roth doesn’t change taxes when I withdraw at retirement).

Anything else I should know?