I'm not doing the BA (Global), but I can offer some advice.
Personally, I've never understood the purpose of the BA (Global). Everything you're required to do in that degree can easily be done in a regular BA (i.e., majoring in International Studies and studying abroad). The BA (Global) also has more compulsory subjects and restrictions than a regular BA. For example, if it turns out you don't like International Studies after your first year in the BA (Global) and decide that you don't want to pursue it further, then you need to go through the whole process of changing degrees. However, in a regular BA, you can easily change your major if it turns out you don't like International Studies.
But really, the big joke of the BA (Global) for me is the compulsory study abroad component. I've always seen that as a means for Monash to get students through the doors of their failing international campuses, since they're obviously struggling to get their Australian students to go to them. Having said that though, I've studied abroad as part of my regular BA at Monash and I had a terrific time; I just don't see any reason for it to be made compulsory.
tl;dr: just do a regular BA. If you really want to study abroad and major in International Studies, then you can do all of that in a regular BA without all the restrictions. Neither degree is more "prestigious" than the other, at least I don't think so.
2 .I know that you are forced to do an International Studies major, but could I also do a second major by combining other units?
You can.