Balancing contribution limits — Solo 401k, Roth Solo 401k, and IRAs

[RusticBohemian]

Is there any reason why a small business owner couldn't have both a Solo 401k, Roth Solo 401k, IRA, and Roth IRA?

If this is allowed, are the contribution limits at all linked?

So a 401k gets funded by both:

--Employer side (25% of compensation, not to exceed $55,000) and
--Employee side (Up to $19k)

But I imagine you could not also open a ROTH SOLO 401k and fund that one also. Would you split the contribution limit between them?

And then what about regular IRAS and Roth IRAS? Can you have two of those as well and fund them fully?

[erutio]

The Solo 401k and Roth Solo 401k share the same $19500/$57000 limits in 2020.  Of note, the solo 401k's also share the same $19500 limits for employees with a 401k from a W-2 employer. 

The IRA and roth IRA share the same $6000 limit.