Link to new law: https://leg.colorado.gov/sites/default/files/documents/2024A...

And are they legally allow to do so without any signed document from the seller or at least hire them to do title work?

A lot of accountants now say that it is perfectly fine as long as it is documented as an arms length business like transaction.  

Have you look at your mortgage documents to see if there is a due on sale clause if not?

I think there is an overall misconception.If you don't receive a tax document(1099) does not mean that there was no taxable income to you.

Go to Etsy and search for "rental property tracker," and you will find hundreds of nice spreadsheets to track 10-20 rentals, usually for under $10.Software has extremely helpful features like online payments, marketing syndication (click a button, and your property is advertised on multiple sites), electronic document review/signing, maintenance tracking, and owner reports.

What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

Separating Y and taxing it as an S Corp could be beneficial if you're looking to take advantage of those tax savings, but only if Y's profits justify the additional administrative burden.Rental Agreement for Home Office:Yes, you can lease your home office space to your LLCs, but it’s crucial to keep everything documented and ensure the rent charged is fair market value.

Document the transaction clearly and consult a tax advisor to ensure the structure is compliant and minimizes tax liabilities.4.

The potential issue is documenting your intent.