Side question:

If I contribute $6,000 to a separate Roth IRA in a year, does that count towards the yearly 401k total maximum?

So if I contributed $19,000 to the 401k, the company adds 4K, this brings that to $23,000. Then if I put in $6,000 into a Roth, that brings it to $29,000. Can I Mega Backdoor Roth $26,000 or $31,000?

So the total of all of this would be $61,000 with the regular $6,000 Roth contribution. Would this be allowed? Or do I need to switch to a taxable account after $55,000 including all totals of the 401k, the match, the Roth, and Mega Backdoor?