I want to rollover my IRA into a solo 401k (I'm self employed) and borrow against the 401k for real estate ventures.

Rolling over your former employer 401k to an SDIRA or Solo 401k is not a taxable event as it's a direct rollover. 

You MUST claim in it 2018...even it at the very minimum it get's carried over as a roll over non-operating loss in 2019. 

Hi there,
I'm new to the world of real estate investing and fix & flip endeavors. I'm currently funding my business through ROBS and I am in search of a CPA well-versed in these domains. I need guidance on how to...

Your "workplace investments" are likely not available until the employer becomes a past employer so a rollover from those accounts are probably not part of the conversation.  2. 

You would probably need to issue a W-2 for your wife.On $100K, it likely will not provide a huge benefit to add your wife, as you would likely not max out contributions in your own name, but having her as a documented employee of the company would allow her to rollover existing savings from another retirement plan into the account.

@Victoria Creighton, My understanding is that the pro-rata rule applies to ALL IRAs with pre-tax funds, including rollover IRAs.  

Hi Andrew,I have been researching my options for my rollover 401K from previous employment to do real estate investment as well.

Following are the similarities and differences between the solo 401k and the self-directed IRA.The Self-Directed IRA and Solo 401k Similarities Both were created by congress for individuals to save for retirement;Both may be invested in alternative investments such as real estate, precious metals tax liens, promissory notes, private company shares, and stocks and mutual funds, to name a few;Both allow for Roth contributions;Both are subject to prohibited transaction rules;Both are subject to federal taxes at time of distribution;Both allow for checkbook control for placing alternative investments;Both may be invested in annuities;Both are protected from creditors;Both allow for nondeductible contributions; andBoth are prohibited from investing in assets listed under I.R.C. 408(m).The Self-Directed IRA and Solo 401k DifferencesIn order to open a solo 401k, self-employment, whether on a part-time or full-time basis, is required;To open a self-directed IRA, self-employment income is not required;In order to gain IRA checkbook control over the self-directed IRA funds, a limited liability company (IRA LLC) must be utilized;The solo 401k allows for checkbook control from the onset;The solo 401k allows for personal loan known as a solo 401k loan;It is prohibited to borrow from your IRA;The Solo 401k may be invested in life insurance;The self-directed IRA may not be invested in life insurance;The solo 401k allow for high contribution amounts (for 2016; the solo 401k contribution limit is $53,000, whereas the self-directed IRA contribution limit is $5,500);The solo 401k business owner can serve as trustee of the solo 401k;The self-directed IRA participant/owner may not serve as trustee or custodian of her IRA; instead, a trust company or bank institution is required;When distributions commence from the solo 401k a mandatory 20% of federal taxes must be withheld from each distribution and submitted electronically to the IRS by the 15th of the month following the date of each distribution;Rollovers and/or transfers from IRAs or qualified plans (e.g., former employer 401k) to a solo 401k are not reported on Form 5498, but rather on Form 5500-EZ, but only if the air market value of the solo 401k exceeds $250K as of the end of the plan year (generally 12/31);When funds are rolled over or transferred from an IRA or 401k to a self-directed IRA, the amount deposited into the self-directed IRA is reported on Form 5498 by the receiving self-directed IRA custodian by May of the year following the rollover/transfer.Rollovers (provided the 60 day rollover window is satisfied) from an IRA to a Solo 401k or self-directed IRA are reported on lines 15a and 15b of Form 1040;Pre-tax IRA contributions on reported on line 32 of Form 1040;Pre-tax solo 401k contributions are reported on line 28 of Form 1040;Roth solo 401k funds are subject to RMDs;A Roth 401k may be transferred to a Roth IRA (Note that from a planning perspective, it may be advantageous to transfer Roth Solo 401k funds to a Roth IRA before turning age 70 ½ in order to escape the Roth RMD requirement applicable to Roth 401k contributions including Roth Solo 401k contributions and earnings.)

The question is how much do you make and could that result in significant contributions to such a plan.If you are just starting out, and have minimal contribution capacity and/or limited resources to rollover from prior retirement plans, then a self-directed Solo 401k is probably not going to benefit you.