US expat transferring assets to UK - financial and tax advice urgently needed

I am a US expat living in the UK urgently in need of financial advice please.

My questions revolve around the following topics: international taxes, capital gains, income tax, residency (I was formerly a resident of California), state taxes, property tax, deductions, repatriation, etc.

I have just had an offer accepted on a property in London and the process is moving quickly. I will need to sell the majority of my stock portfolio in the US and transfer the equivalent of around £130,000 or more to the UK. Some of my questions include:

1) What financial and US/UK tax considerations do I need to be aware of in liquidating US-based sequrities and transferring cash assets to the UK? 
2) What is the best way to do the transfer (and is there an ideal time in the buying process to make the transfer)?
3) What implications are there for US and UK taxes of owning (and potentially someday renting out) property in the UK?
4) I don't believe I need to file UK taxes (I make £90k) and never have in the nearly 4 years I've lived in the UK. However, do I need to report my foreign (US) accounts and securities (and dividends) to HMRC? Does that change after I've lived here for 6 years or something? Should those securities be moved entirely to the UK if I plan to stay indefinitely?

Other questions:
a) I paid UK tax on my wages of only 14.8%. I've regularly siphoned off ~20% of my income via salary sacrifice into my pension; could that be sufficient to explain the low effective tax rate in the UK?
b) Is it allowed to renew my driving license in Michigan (where my parents live and I would have to show residency to get the license) if I'm an expat? Is there any state tax implication of doing so?

Notes:
- I plan on living in the United Kingdom indefinitely.
- I recently re-registered to vote in Michigan.
- I believe I am exempt from California taxes.
(I was most recently a resident of California, where I have voted and held a driver's license (set to expire this month), and still hold some financial accounts. I visited CA recently for 2 weeks after being away for 3 years and moved to the UK in 2016 holding a Type 2 UK Visa with an employment contract in the UK for my previous employer, which I believe qualifies me for Safe Harbour. I have therefore not filed California state tax forms for 2017 or 2018, and similarly do not plan to file them in the future, even if I have bank accounts, voter registration, and my family/closest US ties in California.)

THANK YOU!!

4) I don't believe I need to file UK taxes (I make £90k) and never have in the nearly 4 years I've lived in the UK. However, do I need to report my foreign (US) accounts and securities (and dividends) to HMRC? Does that change after I've lived here for 6 years or something? Should those securities be moved entirely to the UK if I plan to stay indefinitely?

Since you have foreign income you should have been filing UK self assessment  returns every year you have lived in the UK as the UK taxes on worldwide income.  Presumably you have been filing US taxes every year you have been living in the UK , declaring your UK wages and income and either taking exclusions or foreign tax credits to offset the UK taxes paid.

Once you have your taxes in order it is easy to sell securities in the USA, pay UK and US taxes on the gains, and then transfer the proceeds to the UK tax free to buy a house. This is what we did a couple of years ago.

As I understand it, and I am not a tax pro:

If your income is California source income, you should have been filing Calif non-resident tax forms every year to report it. (Unless you were retired and it is retirement accounts income.) Except for California-source income, California does not tax the income of non-residents. 

If you were voting in state and local elections in California (not just Federal) after you left, they could potentially put a claim on your being a resident for tax purposes, as you keep bank accounts there and have not turned in your Calif DL.  https://www.ftb.ca.gov/forms/2018/18_1031.pdf   If you were not voting in state/local elections, voting in Federal elections should have no bearing on your residency status in California.

Your California driving license became invalid when you moved out of the state and took up residence in the UK. (Unless you are military.)

Here's the URL to the Michigan DMV info  https://www.michigan.gov/sos/0,4670,7-127-1627_8669_9040_9042_47086---,00.html 

Here's the URL for Michigan income tax   https://www.michigan.gov/taxes/0,4676,7-238-43513---,00.html  and this one is more specific https://www.michigan.gov/documents/taxes/Michigan_Return_Determination_645347_7.pdf
 
UK taxes - I believe your world-wide income is taxed only if you are a resident. So you should have been reporting your non-UK income every year. Just as you will have been filing US income tax forms every year.

I'll have to leave it to the heavy hitters regarding your other questions. Good luck with the house!

In the UK for tax purposes, are you on the arising basis or have you declared you are on the remittance basis? Answers to your questions will vary accordingly. You may be correct on your assumptions, or you may be very wrong, depending on which method is used.

California, your last residence, is a very sticky state. Driving license, financial accounts - if you ever intend to return to California, you need to check tax obligations carefully.

If remittance basis, you may not claim a personal allowance. £90,000/yr. minus 20% for pension contributions would most likely leave an effective tax rate higher than 14.8%. A discussion about how effective tax rates are computed would be of interest.

You have hopefully been reporting the pension plan on both an FBAR & 8938. Have you been reporting the sacrifice as currently US taxable income, or alternatively electing to claim the US/UK treaty?

Hi all - this is very helpful information, thank you so much!

I'm just starting to swim through what I've discovered are very deep, very unwelcoming waters that I think I have thoroughly muddled already.

I haven't ever filed 8938 (not aware of this one) but I have done FBAR.
I think I just claimed the US/UK treaty?

Thanks again all.