On top of those 'three jobs' we've got 5 kids aged 7-11 between the two of us. 

I wish I found out about real estate investment when I was your age. 

You should always screen every person above the age of 18.

In addition, employer contributions may be withdrawn upon the occurrence of any of the following events:1) The occurrence of a Hardship,2) The attainment of age 59 ½3) The employer contributions being withdrawn have been accumulated in the solo 401k plan for at least 2 years; or4) The participant has participated in the solo 401k plan for at least 5 years.Salary Deferrals(employee contributions): Any employee contribution (including any earnings on such amounts)may not be distributed prior to the solo 401k participant’s severance from employment, death, or disability.

Depending on the age and the size it may require UDOT and hazmat permits, or may be barred from moving it in the first place. 

Our standard policy for all our properties has been that all adults age 18 and over who will reside in the home must apply, be approved, and be a signer on the lease.

@Cedrick Layton You might want to start with the age/complexity of the house first.  

@Matthew Burns Elenis is abolutley right, starting at your age you are going to be serious Pro in 10 years.  

Two distinct income sources that must be separated to be able to assess the true value of a property.

If these features in your unit pale in comparison (age, condition, etc.) to the others, it puts you at a competitive disadvantage.