I'm planning to do Ext 2 English Ext 2 is pretty awesome but you have to be committed to completing all the course requirements or else there's not much point to it. It's pretty much you composing your own work in the area of english you're most interested in be it narrative writing, critical analysis, etc. And it scales incredibly well too . I heard that ext hist is pretty good too but its a lot of work - don't really know much about it
I'm planing on doing Ext 2 english. One of my friends is doind Ext History and from what i can gather you study those who write history and do a major study/assignment if your interested in doing History Ext go to the HSC thread on this.
Multiple projects are fine SO LONG AS YOUR ORGANISED AND START EARLY. If not, year 12 will become living hell around term 3. History extension is fantastic (if you like history).