Solo 401K and 401K Roth sub-account

[Heather Gipson]

Hello all - I am looking to transfer my IRA's from a brokerage firm into a SD 401K with checkbook control. Currently 5% of my accounts are 'cash' and 95% are Traditional IRA's.

I'm wondering if I should put the 5% into a 401K Roth sub-account?  I understand the Roth contributions and gains are Tax free which is very appealing.  

1 - Is there a downside to doing this? 

2 - Do I need 2 401K 'checkbooks' for this or do I just need to track the contributions and gains very closely for accounting purposes.  (or both :)

I'm in the beginning stages of RE investing and want to set things up as strategically as possible on the front end. Thanks!