Reporting fund portfolio for a Brit

I'm a Brit who's moving to the US in a year for work. I hope you don't mind me asking questions from the "wrong" side but there's probably a lot of relevant expertise here

I have some cash to invest and would prefer to put it in UK funds (e.g. Vanguard LifeStrategy) but I don't want fall foul of PFIC rules when I move, pushing that option off the table. I don't intend to move to the US permanently so I want something that I can keep regardless of which country I'm in (e.g., if I buy a LifeStrategy fund in the US I'll have to sell, maybe at a loss, before returning to the UK to avoid HMRC's punitive taxation).

A portfolio of US-domiciled UK reporting funds is all I can think of for this. So, questions:

1) how does one report dividends/gains on sale from a US fund (e.g. VTI) to HMRC? I've never held fund, let alone one offshore, so I don't know the mechanics of this operation.

2) will the IRS withhold anything while I'm in the UK?

3) given I intend to return to the UK somewhen does the exchange rate risk I'd face (investments in USD, but want to spend GBP) make this a stupid idea?

I have not yet had to file UK taxes as we don't move back until next month but I did hold Vanguard Mutual Funds which I have converted to HMRC Reporting Vanguard ETF's including the one you mention, VTI.  My understanding is that when completing the HMRC self assessment that those funds are treated in the same manner UK funds are treated, including dividends from all stock funds such as VTI (US "qualified dividends").

I don't believe Vanguard will withhold any taxes from the funds when I move back (they don't withhold now)

Exchange rate is a risk of course, currently it is very favorable and I've moved a bunch of money over to the UK this year in readiness for my move.