Thanks for taking the trouble to respond and researching all the valuable links.
My main reason for the post was to elicit the odd gotcha from other users.
It took some time to run through the design rules but in the end LibrePCB defaults were good to use for JLCPCB. When generating the Fabrication Data I selected "Default (layer encoded in the file name) and had separate Drill files for NTPH and PTH holes. I did check the gerber files using the Ucamco viewer.
One thing I did pic up on in the JLC documentation is they place a code on the silkscreen layer to identify your boards. You can opt out of that but at a cost. You can also opt to define where on the board that code is placed which is what I did.
The only problem I had was JLCPCB on line viewer which did not work. Their techies were working it apparently.
To summarise: I successfully submitted my gerber files, they were checked, accepted and now I wait.