I hope you are asking two separate unrelated questions, because there's no point in doing cost segregation for properties held inside your self-directed solo 401k, save for some very rare exceptions.Some of the Bigger Pockets experts who operate reputable costs segregation companies are @Bernard Reisz, @Yonah Weiss and @Julio GonzalezSome of the Bigger Pockets experts who offer Solo 401k administrator services are @Dmitriy Fomichenko, again @Bernard Reisz and @Brian EastmanReach out to them and see if they can help.

Quote from @Mike Sfera: for a duplex, is the BP rent estimate for per unit of combined?

Advice on Layout/Design: For those who have added ADUs, do you recommend standalone units, garage conversions, or a combination of both?

Quote from @Collin Hays:Merchants rarely win chargeback disputes.

An experienced team or partner can also help boost confidence.Providing a combination of a solid commitment letter, proof of funds, and a clear, professional approach signals you’re serious and capable of closing the deal.

And we rarely need to use them.Tenants sign and initial each page of the condition report at signing, we quickly go through the property and let them take as long as they want.Ideally at move out they would sign the condition report, but this is nor normally done. 

Combine that with rates that are near high for this century.  3 things could solve this 1) RE prices fall (that would be bad for me) 2) rents increase a lot without RE prices increasing similarly (this would be bad for tenants) 3) rates fall a lot.  

We do have some landlords request listings on there, but very rarely.

They rarely subscribe and I'd rather have them contact me and so we can base the valuation on the GCI it generates. 

Unless you work in Oil & Gas don't expect to come across many deals with rare earth minerals or oil.