Moving out of the UK in the coming months, what to do with UK Bank Accounts

Hi, I not sure if this is the right subreddit but I would be glad to be pointed to the right one.

My issue is, I am moving out of the UK permanently I have been living here for the past 6-7 years. I have worked full time for the past 2.8 years. I have a good enough savings in three UK Bank accounts Monzo, Santander and Barclays. I have also had a workplace pensions account with Scottish Widows, for 2.8 years since I opened it.

I currently have questions regarding these bank accounts, how long can I access them if I move out of the UK? How easy it is to move the money to the country I am going to(US)? Will I pay transfer charges on them? Do I inform them before moving or after moving?

For my pensions I have come to terms that it is better to keep it here and take it when I reach my retirement age. How do I make sure it doesn’t get lost and that I still know what is going on with it? Do I change my addresses to reflect the out of country one? or do I find a UK address for it?

I welcome other tricky stuff too that I might not have listed.
Thanks to any input that you will give me.