Hi Epox, sorry for the delay of the response.
It's a pleasure to have done a useful plugin, you are welcome. ;)
Talking about your requests, I'm sorry but I can't do what you tell me. Just the tag description with shortcode can be done but because of the plugin architecture (you can use more galleries, exclude/include more tags) I'm not sure if this could be a good idea.
The other features (change post title accordingly to the actual tag, tag description) are really interesting but they are out of this plugin scope: it is more NextGen Gallery (the big one) request related (or another plugin that extends this feature).
So, I'm sorry but this time I can't be really useful :/
Cheers!