Sloaners

It's not letting me edit my post! The 90 days may be incorrect- and replace 'council' with 'register' as that's who you contact within the council (must be a designated register but very easy to verify everything I said on the UK gov website!).  You may only need 28 days but I would call the register and ask about the process.  That's all I did and they were quite lovely about the whole thing
 
Designated register offices: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/224796/DROs_GOV_UK..pdf 
 
Editing to add: feel free to start a new thread @Sloaners as you will likely have other questions and we may have hijacked the OP here! 

You can cancel the K1 and switch to CR-1. I'm not 100% sure of the process but I think a search on this forum will tell you what you need to do. You won't be penalized and I highly recommend CR-1 when having the opportunity to DCF in London.  It was a super easy process for us as @Wuozopo said, they're really nice. Benefit: very quick when using them and a CR-1 offers your spouse the opportunity to hit the ground running upon arrival (ability to work straight away, etc.)
 
Just keep in mind in the UK that you'll need to give notice to the council where you plan to marry- being an international relationship, you'll have to give 90 days notice before you can get married, be interviewed by the council (they'll likely send approval quicker than that though- we got ours within a couple of weeks.) You can move up your ceremony if you want as soon as you're approved. Even if you have to wait the full 90 days, the overall amount of time will still likely be quicker and as mentioned, your spouse won't have to be in limbo in the US waiting to be able to work.

Yes because you have a visa allowing you to live and study in the UK. You aren't just a tourist on a month long holiday. You need six months residency there, but no specific length of marriage.
 
About 10 years ago, the DCF page for the USCIS office in London specifically said student visas didn't count. That information was dropped from the page  and some people here on Visa Journey have successfully done DCF with student visas.

As wuozopo said, they don't require you to be married for a certain amount of time.  We sent our petition in literally the day after we got married and he joined me in the States three months later. 

I don't think London (USCIS or Visa Unit) frowns on much. The process is way easier than you imagine. They aren't dreaming up scenes in their head of why you did something. There are certain requirements, payments, and documents they have to see.  ✔️✔️✔️ APPROVED!
 
Try to avoid the "I think they might think that I thought..." mentality.
In London, they are nice and want you to succeed.

A bunch of approvals for October started rolling in. I know we're still a ways out, but it's exciting to see them starting a new month!

I have been taking flight training while waiting for AOS on K3
You have to get fingerprinted again for the TSA and they will do bckground checks etc...pretty straight forward compared to getting K1 and AOS.
I soloed in Dec, had a baby later that day and have my AOS interview tomorrow.