Seems we're about on the same path, although you my friend are much farther ahead than me. It's quite the rigorous path academically, isn't it? I've barely just started but I expect the real hard work to hit pretty soon.
That's an interesting statistic about the number of graduates who go onto graduate school, but it's not surprising. USF has a mere 45 seats available for their graduate school but every year around double that number of students will compete for it. Very competitive. You don't just slide into the profession of architecture; you have it or you don't.
Oh yeah, it's very rigorous, and competitive; why do you think I stopped participating on this website when I got in? There's no free time at all! XD
In a 5 year B ARCH program, first and second year in B ARCH are somewhat rigorous, but are nothing compared to say, 3rd 4th and 5th, with 3rd and 4th being described as the most difficult/rigorous years by many (YMMV). Expect many all-nighters, lost sleep, abuse of stimulants (your choice; I do not condone the usage of illegal stimulants!), weight gain and or loss, loss of social life outside of school, etc. Basically, you're going to have to be an absolute devotee to the cause, much like a monk or soldier. Oh, and all your other classes will have to take the back seat of the bus relative to STUDIO. You don't "work" in studio as much as LIVE in it. I've known people who don't leave the studio for several days in a row, especially near finals. There's a bunch of other stuff, but I don't want to frighten you away from architecture; the program itself already does a good job of that!
And yes; architecture and archi schools are quite competitive; Rice University, for one, only accepts 30 students per year total, compared to say, 150 or more for typical middle to upper sized B ARCH schools. When it comes to portfolios, some schools are more demanding than others, particularly grad schools. Entry requirements for B ARCH are not as stringent, although some sort of academic portfolio may be helpful (along with other things, such as art, etc).
So yeah, best of luck to you, and I hope you're not in for a surprise once the later years roll by! You're either "IT" or OUT!