This is not an issue of custodial policy, but rather stems from the tax code.  

Compared to an IRA, Solo 401k contribution limits are roughly ten times higher.You can borrow up to $50k from the plan; IRAs do not allow participant loansThere is no custodial requirement for the 401k.You don't need the additional expense and administration of an LLC to have checkbook control.There is a built in-Roth component whereas IRAs are either traditional or Roth, not both.A spouse can also participate in the same Solo 401k plan.The Solo 401k has additional tax benefits over an IRA when investing into real estate using leverage.The penalties for prohibited transactions are less severe, though it's best not to utilize this benefit :)

I'll restate that we never take custody of the funds, but rather wait for them to clear your tenant’s account before we initiate a deposit.

You might want to consider both custodial plans as well as those that offer you checkbook control.

Your insurance will be an expense you'll need to swallow, you are, regardless of the number of "not responsible" signs you put up, in a baliee position with the care, custody and control of the paying customer's vehicle.

My IRA's full vesting name is <account_holder_name>, Legal Owner Via Non-Trust Custodial IRA With AET, which is the sole member of the LLC.

Once the employee deferral is maxed out, then the percentage level drops for the profit sharing contributions, but by that point, you're already more than three times higher than the IRA contribution limit.Unlike IRAs, Solo 401ks do not have a custodial requirement. 

In addition to our in-house counsel, we have consulted with many professionals in the field, including tax attorneys, compliance officers of custodial companies, and IRS enrolled agents.Please show me where the IRS has "blown up" an IRA because the IRA account holder was signing purchase/sales contracts or simply handling expense and income transactions on behalf of and for the exclusive benefit of the IRA.  

However, depending on the types of investments you are planning to make you may want to use IRA owned LLC (aka Checkbook IRA) to gain the checkbook control over your retirement funds and to eliminate the fees (transaction fees, asset based fees, etc.) associated with having custodial SD IRA.In most cases you don't need to do a 1031 tax deferred exchange in an IRA when selling a property because an IRA is already tax-deferred vehicle. 

Most non-custodial parents who have court order childsupport have it garnished directly from their paycheck so it should show on the check stub.