Edit: Let me clarfiy that. Not only will potions with the same name not stack, but all Fortify Smithing potions will not stack with one another. Whichever is highest takes precedence. I think all Fortify Skill potions work this way. Enchantments that fortify a skill will stack though, and they'll stack with a single potion.
no they dont stack but you could take a fortify restoration potion which will enhance the stats on your +smithing gear. just make sure you reequip it after taking the potion. using alchemy gear and using mentioned potions you can get really hight fortify enchanting potions.
its as game breaking as the potions from morrwind really...
yes. mix a fortify restoration potion with your alchemy gear and take it and you'll notice that the gear now shoudl give +66% just reequip and craft a new potion and so on... yes, that is an exploit and a big one, which should be fixed imho.
they obviously tried to limit the value on the potions and on the gear but seem to have missed the restoration poitions having an effect on enchantments. otherwise you can't get higher than +29 % and +32% for potions.