PV confused as to how many ac isolators im fitting

[Lurch]

would the ac feed from the pv not remain live at all?

If the inverter sees the grid supply drop it will stop producing so the AC feed will never produce without first receiving power from the grid (outside of standard disconnection times).

is there any problem with wiring the ac isolator before the meter?

From an electrical POV it makes no difference at all. MCS rules may specify something, not sure why it needs fitting at all TBH.