After 3 days of struggle, which I didn't anticipate, I am happy to say I am hooked on piwigo!
The problems were all due to my antiquated ISP hosting, with •PHP: 5.2.9 in Safe Mode and •mysql: 5.0.77
I have previously used 'fotopic' (which abruptly closed down) and then 'pikfu' (which is also about to close) and I then looked at other options such as Smugmug and Zenfolio.
In those 3 days I have learnt a lot about the structure and function of piwigo which was good preparation so that I have been able to launch into loading my 8,000 images confident that it will work.
In particular I like the flexibility and options that I hoped for from piwigo, down to the user being able to customize things and I can see the potential of the plugins too, building on other peoples work.
Now I can't wait for 2.4 in order to assess the product properly!