I have funds in a 401-k plan from a former employer that I want to roll over to a solo 401-k; then, write a check to purchase an income producing property without financing. 

You can avoid the taxation by doing a direct rollover of funds and then buy investment property inside of your SDIRA.

I'm a 34 y/o physician just getting started with improving my personal finances.Need recommendations about investment options for my roll over IRA.Should I go for 100% investment in VTSAX vs. adding an international index fund ( which one and how much %) in my portfolio.

He might also want to do the math each year on tax brackets, and do Roth IRA rollovers each year up to the next tax bracket.

Although uncommon, I know the IRS code will allow me to do an in service roll over of my 457 money into a solo 401k however Nationwide is telling me that it is not allowed.

Would it be possible to rollover/convert an Roth IRA into an self directed IRA?

I have had other investors recommend a line of credit but I seem to be finding that it would still operate the same when I try to roll over that credit into permanent financing in regards to LTV and the seasoning period..

I'll rollover the average cost into the rent. 

I could take a loan against my 401k, pay off her loan, and wait for her to rollover her 401k to her new employer so she can take a new loan out.

I expect to finish this project July-August of 2020 than refinance right after so you'll have your money back by September, But if you would like you can roll over your investment into my next project, also new construction in Kent WA, I should get permits by September and will start building in Kent right after.