I'd suggest that the Mods button should go between "Training" and "Single Player" since any selected mod is likely to affect the Single Player option (different single player campaigns for example) but the tutorial won't be affected.
But if the scripting language goes well a mod might very well have mod-specific tutorials.
(Repeating from the old forum)
The primary game menu should look bog standard except for a title somewhere somehow that says "Homeworld: Old School" (or something) and a small button marked "Homeworld: Advanced" (or something.)
When pressed this would bring up a version of the menu that not only has the mods button, but has advanced game options that can be activated to enhance the standard game.
Thus the player would intuitively go from standard HW ( a "compatibilty mode" sort of deal) to standard homeworld with advanced system and game options (like advanced graphics, engine changes that are more than fixes but less than mods, single player maps etc).
And then on to full blown mods.
This layer cake is a bit more than what even games with standard mod options do, but usually the mod option in a game is an afterthought and everything
gets crammed under "mods".
We can avoid that.
As to where the "advanced" button should go: near or integrated with the "Homeworld: Old School" or whatever would do. If done as a button on the menu then at the top of the choices (not so good) or to the side (should work well that way for all implementations.)
(As an aside what should the button name be? "Mods", "Modifications", "Plug-ins", "Themes", "Game"?)
<The zapkitty gets cheeky...>
A small version of the homesource logo