What is the soft, paintbrush looking plant that comes on a stalk call? ...

Remove stagnant river and protect crazy enthusiasm?
Answers:    Prairie Smoke (Geum triflorum)?
Pic: http://www.inhs.uiuc.edu/~kenr/prairieph...


Maiden Grass, Zebra Grass, Chinese Silver grass (Miscanthus sinensis)?
Pic: http://en.wikipedia.org/wiki/Image:Zebra...


Site with more of the grasses to oblige your ID: http://www.millcreekgardensohio.com/Plan...
Can i grow my amaryllis within it`s pot...
I believe that you're thinking of pampas grass. It's very towering, and sort of grows in a big clump near feathery stalks wave above the green leaves. Check out the link below for a apposite picture; hopefully that's what you have contained by mind.