OK, still sorting this out

Bear with me here - I could really use some advice here.

I'm a US citizen in the UK, hopefully permanently if everything works out. I am retired on a modest pension from a California university, which is a state entity. So far I've no earned income in the UK. I also have a 403B savings/retirement account. I withdrew about $10K total out of the 403B (in two equal sums) and deposited into my Calif bank to pay off my Calif bank  loans/credit cards in August. I don't intend to access the balance of the 403B for several years, if all goes well. Except for student loans, I am now debt free.

Questions:

I arrived April 30 2017. Thus, my first UK taxes, if any are due, are not due until Dec 2018, for the tax year April 2017-April 2018, correct?

If I owe UK taxes, I will need to file a self-assessment by Dec 2018 and can then take anything I have to pay in tax to the UK off my USA taxes due on the tax return for Jan 1 - Dec 31 2018?

I know I have to pay the IRS for Jan 1 - Dec 31 2017, and pay California State taxes for Jan 1- April 29 2017 only. I will have into June 2018 to file a return, due to the automatic extension for overseas persons?

I hope to be able to use TurboTax, as it's not steered me wrong for years now. So hopefully it will guide me through it all, but....

My University pension will be taxed only in Calif, since it's from state sources? I believe that I do not pay tax on the pension to HMRC due to the provisions of the tax treaty. If that is the case, do I need to even report the Calif pension to HMRC?

On the distributions to pay off the Calif credit cards - is this amount taxable in the UK, since the money did not come to the UK even though I was resident in the UK? (Fidelity already withheld 20% to cover USA taxes.)

I keep seeing bits about reporting interest on investments. I'm a small-timer, but do have the 403B that is making me a few hundred a year.  Do I have to report to HMRC the interest earned on that account if it is not actually disbursed to me? Or do I have to report it as income in the year it's earned even if it stays in the 403B?

When I finally decide to draw US social security, with the tax treaty I pay tax on it to the UK and not the USA. Do I even report it to the IRS?

Thanks.

Hope someone who remembers this stuff better posts. I am not sure at all.....but it seems the state pension topic has come up before. I could easily be wrong but it seems the CA pension wasn't considered a Govt pension. I think I messed up last year and didn't fill out a self assessment (by advice on the phone from the tax assessment person I called). They had told me I didn't need to do one until I started my Social Security in a couple of years. I am on a US Govt pension and not a State Govt pension.