Some year ago the choice of items was limited, it was pretty much only Calypso items and only one "generation" of (L) items (Breer m1(L), Breer m2(L) etc), so once you knew your level it was pretty easy to keep track what to look out for. Now there are zillions of new items, many at same:ish level, and from different planets.
As for weapons with different levels; let the highest level Count (just to make a definition). Today as far as I know items with more than one level is the same (ie (hit) and (dmg) for weapons).