Hi-poly is a name for something what's not going to be used in a game, something over million polys, like sculpt in Zbrush, there is no polys limits.
Low-poly on weapons and characters depends on what kind of game is it. Characters can be starting from 1000 - 2000 for mobile games and easily reaching 50 000 tris and more for fancy next-gen game. I'd say standard range for most games is is 10.000 +-
For weapons range is pretty wide as well can be 100 or 5k or even more. Basically everything what goes in a game can be called low-poly.
You can get all answers on your questions from free book with tutorial and wip for this sword here: [link] Since it's an old tutorial, I can tell that I use 3D coat for last year instead of trial attempt of using Mudbox
Every time I look at your work, it makes me feel so ashamed of Blizzard Entertainment for not hiring you. This sword model (and especially the texture) is better looking than every single weapon in World of Warcraft.