She is 6 months into an 18 month lease and this lease is super tight.

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).Solo 401k vs.

If there truly are no rehabs to be found, rentals are in high demand at high prices, and the supply of new homes is tight, building new might make sense.

Our REA has two other investors that have made offers and tonight is the deadline before the seller chooses someone.

It can be an advantage to you as @Austin Andrews says because the 1031 has some pretty tight timelines for the seller to meet. 

The response didn’t give a deadline for my best and final which confused me because in the past I have always been told 48 hours.  

If your deal's that tight, you don't have a deal.It's okay to keep a little money in a BRRRR deal, just dump the cash flow back at the HELOC in the beginning to pay it off.

If you have plenty of income and your DTI is really low then it will be less of an issue, however if your DTI is tight then you might want to take the lowest rate and longest term auto loan you can get to push that monthly payment down.

Cash flow will be tight, especially on the higher end, but with depreciation expense and principle pay down, you should be able to make the numbers work.  

Pay them once the job is done and inspected and give them a deadline.