I flew Mersey Gateway from Wigg Island, but you could also fly from the Trans Pennine Trail / Spike Island.
Fiddler’s Ferry Power Station was flown from the Trans Pennine Trail. The Dream is straightforward.
The Wind Farm at Frodsham requires a bit more care - I parked on the track (Hares Lane) that leads down to the hovercraft circuit, there’s a model flying club based next to the circuit itself so best to stay clear of that.
Another option near you is Sankey Viaduct, there’s a nice area of grass south of it that I flew from without any problems.
All these are outside the Liverpool Airport No-Fly Zone.
Regarding other legalities: stay 50m away from any vehicles or structures; all of these should also be 150m away from “congested areas”. Several of these are technically private land (e.g. owned by the local council) but with permitted public access; if you fly when areas are not busy (e.g. first thing in the morning), and stay considerate of park or path users, you shouldn’t expect any trouble. The only one of these to avoid if you are unsure is Fiddler’s Ferry, where there’s a remote chance somebody could report you to the police, who could question you under S43 of the Terrorism Act 2000, but that’s pretty remote.