I don't know of a FAQ thread on site but here is a few thinks I suggested to my daughter as she prepared to move back last year after 35 years away. (No particular order, just things to consider)
1. Create a Wise.com account, linked to your US bank with 2 currency accounts, in USD and GBP. It will provide US and a UK Routing and account numbers. Very easy to bring money to England plus you can get a Wise GBP debit card to use while you build a credit score and get a UK credit card.
2. Create an online IRS account if you don't have one - much easier to do before moving back. 2FA can be via an authentication app called id.me which is what I use.
3. Create an online Social Security account if you don't have one. Again, much easier to do so while in the USA, 2FA via email.
4. When eventually you claim SS you will be asked if you are a USC and if not have to send in your US passport as proof. Much easier to do so while still in the USA, walk into a SS office. I made the wrong assumption that registering citizenship status with my employer, applying for a US passport, filing US taxes for many years as a USC, and also proving that I was a USC to apply for health insurance was enough. When we did apply to start SS through the US Embassy we had send in our passports to get the SSA to have us on record as USCs. (Even though payment of SS benefits is not dependent on being a USC)
5. Move any 401k employer plans to an IRA or check that you can full access to your company plans from overseas. This is a non-taxable event. When our son moved back in 2017 he quit his job in Texas and initiated the process, which completed after he arrived in the UK but it all worked well.
6. Have a forwarding US address if necessary. I keep a US credit card linked to a US PO Box so that I can buy TurboTax each year.
7. Add voice recognition and/or check how 2FA is set up for all US financial accounts. Vanguard accepts UK phone numbers as does our US bank (HSC) but many don't.
8. Convert mutual funds to their ETF equivalents where you can - this is a non-taxable event in most cases. Retirement accounts are no problem. After tax accounts mean no qualified dividends or capital gains from MFs but Vanguard ETFs and hundreds of others are recognized by HMRC. If you have MFs with a blend of stocks and bonds then all dividends will be taxed by HMRC as regular income, but no excessive PFIC style taxes and penalties.
9. US phone number for use in UK. I use a Skype number but there are other options. (All US toll-free numbers are free which is useful for calling banks, credit card companies etc)
10. Car insurance no claims statement and keep a copy of your last insurance certificate. Aviva will accept no-claims notices from the US, but most others won't.
11. Bring along copies of medical records and prescriptions
12. When you arrive you may want to look into private health insurance and we found the folks at Active Quote to be really good.
https://www.activequote.com/Fire away with more questions, I'm sure others will have some good advice