It took me about 350. Of course, it's highly variable based on such factors as rested/wellrested/loverscomfort bonusses, mage stone, how much disenchanting you do...
And the two enchants per item perk at 100 skill doesn't mention that you take a few points penalty on each (instead of the +28 each on smithing or alchemy, I get a pair of +25's - and that's after using a potion good for an extra 30% boost). I haven't checked what I get for weapon skills, yet.
No, it does 28 (at 100skill+25%potion with perks). if you got 25's that's because your potion ran out before you locked in the enchant. The timer keeps ticking even when you're entering your item's name.