The ottava sign is combined with a horizontal line over all the notes affected, with a vertical "tail" to signify the end. All the notes under the line are played up an octave.
As far as noting your exercises in concert pitch goes, you could do it that way if you wanted to... but you'd probably limit its use. I've seen guitar parts noted in concert pitch, which requires alternating between bass and treble clefs. I even practice them sometimes, but not often - but they're not standard, so you'll only run into them a handful of times in a whole career of reading. Only a few instruments (bassoon, trombone, and piano, off the top of my head) change clefs with any regularity, so most people won't be used to reading them. And when I see a score where the parts are written for the convenience of the composer instead of the performers, my gut reaction is that an amateur wrote it.
That's not always the case - I met a professional orchestral composer a few months back who writes everything in concert pitch, and he's had a great deal of success and gets regular commissions. But I had a hard time following his scores, and I'll bet most amateur and semi-pro conductors would too - we're used to seeing things the way we're used to seeing things.
But maybe that's just me. I'm kinda old school in notation - one of the things I did to pay my way through college was writing out charts for jazz bands (by hand - this was pre-Finale days), so I put a lot of effort into learning the differences in notation for various instruments. In my view, music is meant to be performed, so it's worth a little extra effort on the composer/arranger's part to make it as "standard" as possible for the musicians. Make it easy to read, and they're more likely to play it