OldUser

Technically, you are still a legal resident.  However, not having clear evidence of that status would be a gigantic hassle.....even inside the US if you needed it. 

Gotcha. Makes sense to me. I’ll try to see if they’ll give me a new stamp.

True.  Upon entry, all it takes is a CBP agent to trace that current stamp to a denied I-90.  

Tehnically they're accurate. You can travel outside of the US but not come back easily.

I wouldn't trust a Tier 1 USCIS rep.  There is no basis for your current stamp, imo.  The base I-90 was denied. Normally, that voids all associated benefits.  I would still try to get a new ADIT.  Just my opinion.  Others might disagree.

I agree, you should get a new stamp.
 
Good Luck!

The extension letter from the I-751 is no good since it must accompany the expired Green card.  The current letter you have is based on a denied I-90.  I would get a new ADIT stamp...My opinion. 

OK.  The extension letter is worthless without the expired Green Card.  Since the stamp you have was based on a denied I-90, I would get a new ADIT stamp in passport.

Do you have the I-751 extension letter?  Based on your timeline, that should extend your conditional Green card until 2027.    If you do not have your expired Green card and extension letter (received after filing the I-751), I would get a new ADIT stamp. 

You're fine. Don't worry.
Make sure your sponsors file I-865 too (by mail)

There is NO sponsorship for B visas.   None.
 
It is doubtful you will get a B visa in your situation.   

My lawyer told me to have them signed by those people and attach copies of their state ID / DL. To say it was ackward to ask is to say nothing. But friends were very keen on providing it, and my I-751 got approved.
 
Notarizing it may be easier / safer than asking for their IDs.

I know that.  My point was that if she or an agency falsely indicated she was married on that tourist visa application in 2018 (which has been known to happen), it is going to present a big, big problem for the K-1 or a CR-1. 

The truth -always the truth
CO will assume u have immigrant intent as u r single and have weak ties to home
college is not one as u can finish college in the US

There aren't any sponsors for tourist visa. You apply and interview, they decide if you get the visa or not. 

Confused, what do you mean by "it wasn't required"?  You are required to provide a copy of all previous divorce and death certificates , not just the most recent one, in the I-129F petition. USCIS on State side needs to assess your legal status to re-marry. 
 
Did you hide that divorce in the I-129F petition?  

That was my guess and I know there are similar ones but for the life of me can not remember them.
 
A bird in the hand is worth 2 in the bush?

Literal translation:
 
"if you chase after two hares, you will not catch even one"

You're fine. Don't worry.
Make sure your sponsors file I-865 too (by mail)

I don't think such a letter is necessary.  We viewed the application as very impersonal - can you answer yes to all the important yes questions and no to all the important no questions and do you meet all the qualifications? Can you give them the tax info and other documents as required? If yes, then anything more is not needed. I think the large beauty of it is that becoming an American can feel nice, but at the same time rather ordinary. You don't have to explain your whys of wanting to become naturalized.

A lot of people have reported moves later than 10 days.  I have never heard of anyone having issues.  I wouldn't worry about it.
Make sure your petitioner and sponsors mail an I-865 to report the move also.

Do you know the Russian proverb about trying to chase two hares at the same time?
 
You can continue playing games with US residency, but don't be surprised if you lose it.
 
Re-entry permit is what you need for short term. For long term, you'll have to pick. Relying on Germany changing laws is a weak plan.

The simple answer would be to decide which opportunity is the more important to you and go with that.
 
You seem to know the issues otherwise.

Saying 'Had some vacation, been here and there' when you know: a) you are living and working in Germany (which puts the GC in jeopardy, since it's for living in the US and not visiting; and b) you know it's not a vacation.
 
A re-entry permit will protect your LPR status.  And be sure to file your taxes (you likely won't be double-taxed but get a good accountant to assist).

Every couple has their own priorities, and each couple must decide which visa is better for their situation.
K-1 
  More expensive than CR-1
  Requires Adjustment of Status after marriage (expensive and requires a lot of paperwork)
  Spouse can not leave the US until she/he receives approved Advance Parole (approx 6-8 months) 
  Spouse can not work until she/he receives EAD (approx 6-8 months) 
  Some people have had problems with driver licenses, Social Security cards, leases, bank account during this period 
  Spouse will not receive Green Card for many months after Adjustment of Status is filed.
  A K-1 might be a better choice when 18-21 year old children are immigrating also
  In some situations, marriage can affect certain Home country benefits, making a K-1 a better choice 
  A denied K-1 is sent back to USCIS to expire
  K-1 entrant cannot file for citizenship until after having Green Card for 3 years.
  Once an I-129F has been approved, delaying the case is difficult to impossible if the need arises.

CR-1/IR-1
  Less expensive than K-1 
  No Adjustment of Status(I-485, I-131, I-765) required. 
  Spouse can immediately travel outside the US 
  Spouse is authorized to work immediately upon arrival. 
  Spouse receives Social Security Card and Green Card within 2 or 3 weeks after entering the US 
  Opening a bank account, getting a driver's license, etc. are very easily accomplished with GC, SS card, and passport.
  Spouse has legal permanent Resident status IMMEDIATELY upon entry to US.
  The clock for citizenship filing starts immediately upon entry to the US.
  A CR-1/IR-1 case can be delayed indefinitely at NVC if the need arises.