Pulling the second super is just as much as the first, 600-1200. (Or 700-1200, depends on what you believe, but those are just the averages.)

After you pull the 2nd and get the alternative super, and go for the 3rd (also 600-1200) I believe it either switches back to the original or, more likely, it goes back to the random 50/50.

(Of course there's always that chance you'll get lucky and get a super prior to that mark.)

I haven't heard of such a rumor yet, chances are you may have most of, if not all of the rares by the time you pull your super. But as far as I know, it remains the same, the rare counter should not be affected by the super rare counter. You pull a super, then a rare later, the rare can be anyone, if you're still missing someone, you have about a 12.5% chance or so to get them.

So in short, as far as I know, you aren't guaranteed a new rare after pulling your first super.

If we were to really see how many people got a new rare post-super, then we'd have to set up a poll, but then there's the people who already have all the rares prior to getting the super.

I'm just gonna say that every rare is random, you aren't guaranteed a new rare after getting your super. You might get a new rare after your super, but the chances would be...

Tendo, Kage, GNW-12.5%x

Jin1, Jin2, Cloud-50%, if you don't get either of the rares before your super, I...I really don't know how you did it. The 6 Edo Jin treasures would fall into this category, chances are you'll get all the rares prior to the super.

Edo Tensei-25%x, due to the low pulls needed for both rares and supers, you have a chance not to get all the rares on your first run. A good chance at that.

Sage Naruto-33%x

X being the number of rares you're missing.