4) Bosses and other big baddies would need to require potions to defeat. Master vampires, dragons, dremora, bandit chiefs, etc should have you reaching for the drinks like a gamer pulling a caffeine-powered all nighter. If alchemy is going to be a required skill, then potions need to be required.
You just lost me right there. Despite most games' attempts to drown players in a sea of potions, I subscribe to the school of thought which holds that potions are for severe emergencies, not something to be chugged like cheap beer at a frat party.
For reference, I've just retired a level 68 stealth archer with 200+ hours of play time; I don't think he's used more than about a dozen healing potions total in his lifetime, plus maybe four or five Fortify Smithing/Enchanting potions and that's it. Neither he, nor my mage character (about 40 hours in), nor my axe-and-shield melee fighter (at 10 hours) have
ever used a magicka or stamina potion. If you give me a boss that "requires potions to defeat", I'll most likely first try a few different tactics to see whether I can find a way to beat him without taking up potionaholism, then call in a companion to see if that helps, then finally either run off to come back and roflstomp him in a few levels (if the situation allows it) or open the console, turn on immortal mode, and wear him down that way (if the fight is rigged to prevent retreat). I absolutely reject the notion that, if you're not downing 47 potions to get through every fight, then you're not trying hard enough.
As for what's already in Skyrim, there are money sinks, it's called high level training. Training any skill past 70 requires quite a bit of gold.
Seriously, this is one of the major things hindering any attempts to balance the economy in TES games. I choose to level my skills solely by using them, to the point that I often forget that buying training is even in the game. Other players use trainers constantly to boost their skills. Anything that prevents me from amassing huge piles of gold will pretty thoroughly screw over a player who invests in training. (Somewhat ironically, a big part of the reason I first decided against training back in the Daggerfall days was that the ready availability of cash made it feel too easy to just buy a high skill level.)
Count me among those who think the best solution is to provide more options for spending large piles of gold on building or improving things. Building a fortress in the wilderness, rebuilding Helgen, or fortifying Winterhold are all excellent ideas from earlier posts and they also all happen to be things which would logically lead to upkeep costs for maintenance.
Smaller things like equipment maintenance or forcing players to buy potions, well... that retiring level 68 has over a million gold on him. Even buying a hundred Ultimate Health Potions and being forced to re-upgrade his gear every day of game-time would still barely be pocket change compared to that.