Sorry, can't help much recommending where to go, but we did the same as lightning running ours in (almost there at the 20 hour mark) - canal, bit of river, bit of Bristol floating harbour - the latter where we were able to get up to full revs as recommended.
As far as pressure gauges go, I've been eyeing this one up this afternoon...
available from a number of places at about the same price. It looks like it fits between the valve and the hose from the pump, so ideal for the last few strokes with the handpump when finishing it off, I reckon.
Anyone else using one of these ?