@CP01
Sure, you can do that. I have 403b funds from my old employer, pre-tax 403b from my current employer, after-tax (Roth) 403b from my current employer, and a Roth IRA. They all happen to be with the same broker, so I don't need multiple apps, but your accounts are only limited by what you want to keep track of.
The only way to clear the mixed traditional IRA situation is to convert it to a Roth IRA. You will pay tax on a pro-rated basis (if 20% of the account is after-tax, you would pay tax on 80% of the conversion). Whether you convert or not depends on what your tax rate is today vs what you think your tax rate will be when you retire. For which you need a crystal ball. But there is no harm in leaving the mixed traditional IRA alone until you retire. You will only generate a new form 8606 if you add or withdraw funds from the traditional IRA during a particular year. So you will want to keep the most recent one, whatever year that is, even if a new one is not generated.
There will be an income level where you can't contribute to a Roth IRA any more. The income limits for 2025 and 2026 are here,
https://skloff.com/ira-contribution-and-income-limits-for-2025-and-2026/
If your income reaches the limit where a Roth IRA is not allowed, and you have not maxed out your 401k, go ahead and do that first. If you max out your 401k and still want to contribute to retirement, you will have to add more after-tax (non-deductible) money to the traditional IRA, you would be stuck with that as an option at this point.
