@Daniel Dietz & @James R aduna - we done it for 3 SFR, 2 acquired in 2017 and 1 in 2018. All were 3/2 SFRs with an approximate FMV of 200K (I think the tool works best with SFR between 100K and 500K). Each report cost us $400 and, once I got the handle of the online tool, it took me about 15-20min for each. It's easy, you'll need a couple inputs from the CPA (like your tax bracket to give you an estimate on tax savings) and to be clear on the property depreciation basis, the rest is property details the CPA will not know anyway and you'll have to provide (like the length of the fence and material, or the type of flooring).
We kept it simple and did not complicate ourselves with older acquisitions (only the ones in that tax year) as that require a change in the way taxes are calculated, going back and amending returns, etc., extra stuff on the CPA side that he will charge you for. Without that, you just give the report output to the CPA to add it to the tax return.
Last year, for example, we also got a depreciation bonus and accelerated 20K+ with the CSS that got us a serious boost in the tax refund. Keep in mind, that is an acceleration of depreciation, not a save. Still, $400 for 7K+ extra in tax refund, not a bad deal.
Normally, if you end up with losses because of the depreciation and CSS, and your adjusted gross income (AGI) is 100K or less, I think you can move 25K of the losses to the active side of income and reduce your tax footprint. If you have more than 100K, it gets prorated up to 150K AGI. The rest gets stored and you can get it next years (you don't lose it, just gets delayed). OR If you qualify as a real estate professional (not that difficult, if you participate actively in your property management and meet the hours requirement, easy if you have non working spouse that is doing that) than you can deduct more than 25K in one year. A CPA can explain better than me, according to your situation specifics.
How any of this applies to properties in an IRA, converted to a SOLO401K, beats me. You need advice from a CPA here.