Contribute to a Non-Deductible IRA on top of a Solo 401K

I have a question on whether I can still contribute to a separate non-deductible traditional self directed IRA on top of my existing allowable Solo 401K annual contributions and file the non-deductible amount on form 8606?

Answer: Yes the IRS regulations allow for what they call IRA non-deductible contributions. See the following IRS links for more information surrounding this.

https://www.irs.gov/Retirement-Plans/Retirement-Plans-FAQs-regarding-IRAs-Contributions

https://www.irs.gov/Retirement-Plans/IRA-Deduction-Limits

It appears from the IRS website and  that both me and my spouse (although he is contributing to his company's 401K) can do this and the limit for each person is the lower of $5500/yr or our compensation, although we may not be able to deduct the contribution due to AGI limits. Please confirm.

Answer: Your understanding is correct. See following IRS link. https://www.irs.gov/Retirement-Plans/Are-You-Covered-by-an-Employer's-Retirement-Plan%3F

Can we convert this traditional IRA to a Roth IRA anytime? Do we still pay tax if we are contributing a non-deductible amount?

Answer: Yes. When converting non-deductible IRA funds to a Roth IRA, yes taxes are paid on the earnings but not the basis because it is a nondeductibel IRA. However, if you have other traditional IRAs with only pretax money those also have to be converted. In other words,you cannot just choose to convert the non-deductible IRA funds.

Do we set up an LLC and bank accounts and put ourselves as trustee to control the check book account and make investments similar to my Solo 401K account?

Answer: Yes that is an option.

What are the differences between Solo 401K and IRA LLC?

Answer: see following link.
http://www.mysolo401k.net/self-directed-solo-401k-vs-self-directed-ira/

If we qualify, what is the deadline for setting up the IRA LLC and contribution deadline for 2015?

Answer: No deadline applies for the setup of an IRA LLC. However the contribution rules apply to an IRA which means you have until April 15 to make the prior-year IRA contribution.

To learn more about the IRA and Solo 401k contribution rules VISIT HERE.