I've been very happy with Maslins (https://www.maslins.co.uk) in the past. I suggest you give them a call and they'll probably answer a lot of your questions above free of charge.
I was a happy client of Maslins when I switched from sole trader to limited company. I was doing freelance software development so the switch was a doddle. You get a FreeAgent account as part of the deal and they have access to it to oversea your accounts. They will also do your personal self assessment for you too.
I’m sure they will be able to advise on your situation.
I’m sure they will be able to advise on your situation.