Does a transcript analysis to determine the exact date the federal tax debt expires stop the clock on the tax debt?

If you are asking about a statute of limitations for an IRS collection, an answer is not so straightforward. The SOL can be tolled by a few events...

If you can prove ties to your home country, you may be able to obtain a nonimmigrant visa.

What year's Federal Poverty Guideline does USCIS use for I-485 related Affidavit of Support?

If you file your I-864 in 2019, then you should use 2019 Poverty guidelines.

Tax refund and divorce?

You may find helpful info here: https://www.cadivorce.com/california-divorce-guide/what-to-expect/significance-of-the-date-of-separation/

My priority date is Jun 2010 with EB2 , can i apply AOS .

Your attorney is your best counsel since s/he is familiar with the details of your case. Unless you are from China or India, EB-2 visa category is...

I mailed a visa extension i-539 43 days before my i-94 expires will it be considered late filing by the U SCIS?

Your I-539 application should be processed by the USCIS as timely filed.

Can a sole prop owner create an LLC at 2018 year end, elect S corp status and pay taxes on 2018 sole prop income as the S corp?

Taxpayer may complete and file Form 2553: - No more than 2 months and 15 days after the beginning of the tax year the election is to take effect,...

You may refer to the IRS website to find some self-guidance: https://www.irs.gov/pub/irs-pdf/p502.pdf

F1 visa approval?

If you overcome an immigrant intent issue by proving substantial ties to your home country, and if you are excepted to a US school that issued I-20...

If the IRS sends a CP503 notice, with no reasons or calculations given for the taxes it says we owe, what is the best recourse?

You may call IRS to inquire about the balance due. You may request tax transcripts to review it yourself (but it probably won't be clear for you)....