I vote no for item level requirements and no for more merchant items appearing as you level. The former "issue" can be taken care of by making better items hard to get without investing into a particular stat significantly (i.e. a chest in the beginning of the game requiring lockpicking 2 or 3) or without killing monsters way above your level. The latter can be taken care of by making the gold scarce, which it seems to be the case so far.