1) I think that limiting it to "only what you can equip" is fine. The lack of untyped pieces being moggable (such as shirts and a few other cosmetics) seems a bit weird, but could easily be fixed by just retyping the ones that have a visual as cloth.
The inability to change types of armor for what you have equipped could be lifted though, if I understand it properly as outlined. People talk about wearing cloth as a paladin/warrior lot in the thread, but there's plenty of stylish leather pieces a warrior or paladin could use for a cool look too. After 40 that becomes nonviable.
2) Widening the range of weapon types would be a small mistake. Not a big one, but a mistake still. There's a fair number of weapons that share a model but are different types already, and it'd devalue the less-common/harder-to-find ones in favor of the path of least resistance.
Unifying 1) and 2), opening "everyone can use everything" up I think actually can devalue some of the mog hunting. Cosmetic mog-focused items being available from rep, events, turnins, hidden or long questlines, or as rare (additional, not replacement) drops from bosses and trash mobs would be wonderful and not out of the spirit of Vanilla. For example, the defias mask and the parrot and siamese companions from the deadmines, as well as other various cosmetics in the world (orb of deception, fish weapons...). For the aforementioned gardener mage, a "staff shovel" could be something to look for in world if added. That would fill a big gap for that specific item model.
For completeness sake I'll also say that well-known iconic items shouldn't be devalued by an easier-to-get cosmetic intermediary. Meaning no 'replica' raid gear, no "counts as a hammer" brightwood staff, etc. As well, faction-specific appearances should probably be the exception and not common. No ironforge-emblem shields for horde. A few items that you get from killing enemy-faction mobs in quest areas already exist to provide a small amount of flavor there, no need to make it common.
Basically, no need for Twow to start to look like maplestory
Finally,
3) I think the pattern established by the level 10 and 20 turnins could be just repeated. 5 of the appropriate cloth, 5 of that tier of leather, 5 of the most common, lowest value gem from that tier of mining, and 5 of a specific common cross-continent monster drop. As it stands you're kind of punished for not getting your mog tokens in at the 10-29 range when it's much much easier, and less costly relative to the level range. At 14, collecting the mats for the tokens cost less than it takes to get enough silver to buy a single skill. At 60 it costs far more and you have to travel much farther to farm the pieces.
Presently the middle of the range requires some esoteric crafted items that aren't even normal trainer recipes. Good for crafters to make bank due to the low supply, but the low demand limits things somewhat. They're also not linked to the level ranges at all and seem semi-random.