1. This is planned for v4 (if not 4.0, surely 4.1 or 4.2).
2 & 3 can be added as options in the gallery insertion modal. However, I can also recommend the following solution for now:

a) Create a custom gallery layout (just copy the one you like inside your template's html/jw_sigpro folder - create it if it doesn't exist) and name it X_Random (e.g. Classic_Random). More on that on the "MVC templating..." section in SIGPro's docs: www.joomlaworks.net/support/docs/simple-image-gallery-pro

b) In the new layout's default.php file you can change the ordering to be random and you can set a fixed count to shown thumbnails. Then when embedding a gallery in a module, you can select the new layout from the added drop-down in v3.8.0. This is quite easy and if you're interested I can provide the relevant code through our helpdesk system.

Regarding 2, my point is that you can go beyond ordering and create a unique layout to use as well. That layout can then be uploaded to any new project and be re-used. But of course, it's a deployment preference obviously.

I'll do my best to extend gallery insertion with more control options.

As for having more readable parameters, you're actually right and it's something that should be implemented. Old galleries won't have an issue as the old syntax can still be valid, just not preferred for new galleries.

All noted. Thank you for your feedback :)