IME as long as you get at least 100+ GPH
through the media it will work very well. I've even used it in my Phosban Reactor 150 without issue.
Your plan sounds fine to me
Just keep an eye on it to make sure it doesn't clog your water flow but that shouldn't happen for months. I would do it on a down baffle so if it did clog for some reason it would just spill over and keep your water flowing.
IME using more just prolongs it's usefulness and hasn't been an issue either. I use 3 100ml bags for my 55 gal
and regenerate them about every 4-5 months now.
Interesting thread on Purigen