1. yes, weapon/helm/shield are always att/hp/def

2. short answer, yes. 

you can use glyphs until their possible max stats are added to the item. example: a glyph gives +1-3 Speed, you can use those glyphs until you have achieved +3 on the substat on your items (you cant lower the substat by failing, so once its +2 it will never drop, you can only increase)

ofc you can then use higher ranking glyphs with higher potential substats

3. the Advanced quest rewards reset once you have claimed all rewards

if you just let them sit there without claiming they wont reset

4. the fusion model where you use old rares is pretty much dead, so keeping rares for that is pointless

personally I keep 1 copy of each rare if I ever have the need for one for some specific situation but no need to keep them for potential fusions

With the recent changes to the Arena and the matching done on player power, it is generally better to get rid of any rares that you don't want if you want to overinflate your own power level.  Every champion you have counts towards your power, even if you aren't using them.  This also applies to equipping champions with artifacts that you never use.

Alot of people have found the arena easier by dropping their power levels down to a more reasonable level.

pvp only 4 cheeters

Cheating is definetly not a problem of this game.