Okay here we go.
A degree of success today, thanks.
upload of SVN 734 successful
Ticking one of the templates in the Templates manager > Templates, selects a template and that remains ticked even after leaving page and returning to it.
Template Installer icon still missing though.
After selecting semantic.....(template 2 in list) I went to the front end and clicked Gallery. WooHoo

It works! although something doesn't quite seem right it's there and clickable and the slide show works well.
Gallery displays :-
3 random images
3 Latest images
and 26 thumbnail images over three pages cleanly and as expected but the test gallery info box indicates that the size is 5 images

Problem with uploading new templates however.
I uninstalled the two templates I'd installed as they'd ended up in the normal Joomla template manager

went once again into the RSgallery2 template manager and selected template installer etc. chose superclean and clicked upload and install. It just ended up back in the Joomla template manager again.
That's as far as I've got at this ungodly hour of the day. I will continue to play and upload another folder of images (back end batch upload) and will try some front end uploads too.
Thanks for your efforts, I realise that we have a way to go yet but it's getting there!

View test gallery at
http://ccgi.frizzell.plus.com/nmids/EDIT:
Just tried front end upload. Unless I'm missing something it won't allow it. I'm logged on with super administrator status. No go, that's okay for now as most of the galleries will be multi image done in the back end but front end uploads would be useful in future. Dare I say front end batch uploads???