I would like to roll over funds from a 401K with a previous employer to a solo 401K with the intent to take a personal loan of 50% of the funds.  

The repayment terms for a 401k participant loan are equal monthly/quarterly payments of principal and interest (typically prime plus 1%) over a 5 year term (longer if used to acquire your principal residence).Please note that if you take a full $50,000 and then pay back the loan, you can't take another $50,000 until 12 months after the first loan was fully paid back.Per the loan offset rules that went into effect with the 2018 Tax and Job Act: if you leave your job and the loan is current at the time you leave your job but then the loan goes into default because you left your job, you will have until your tax return deadline (including any timely filed extension) to make the loan current by depositing the outstanding balance into an IRA (and thereby avoid the taxes and penalties that would otherwise apply).Alternative: Rollover Funds to A Solo 401kIf you are self-employed (i.e. active self-employment earned income separate from your w-2 income) with no full-time w-2 employees, you can set up a Solo 401k and then rollover your 401k funds once you leave your current job [NOTE: You generally can't rollover funds that you saved to your current employer plan until you quit.].You could then take a loan of up to 50% of the balance not to exceed $50,000.

Saved up, cashed out my rollover IRA, used part of my work bonus and took equity out of my personal residence... whatever it takes.

Following are some of the similarities and differences between a self-directed IRA and the self-directed solo 401(k) plan:The Self-Directed IRA and Solo 401k SimilaritiesBoth 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;Both 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 2017, the solo 401k contribution limit is $54,000, 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.)

That is why at some late point you will want to roll over a Roth 401k to a Roth IRA.Well asked question Jose and very well calculated after that.

I do not recommend the following strategy, but I have heard some of my buddies discuss it: you can do an extended rollover (not sure of the correct term), where you roll over the money from one custodian to another and they send you the check for 60 days (not sure if it's 60 or more or less).

For example if you want to roll over 401k pre tax funds, you would obviously want to open a traditional IRA.

You would have to rollover/transfer funds from your current retirement account into self-directed.

(You'll learn this when it comes time for a rollover from your current account.)

They educate investors on the process of self-directed investing or assist in setting up single-member LLCs for either “check-book control” or to purchase a franchise or ROBS (Roll-Over Business Startup).