[*]No limit on how many magic items you can use. No milestones.
One thing you could consider is requiring them to take a solid enough hit to die. This 3-part article about taking shortcuts with HP tracking for monsters suggests level+3 as the threshold. Or maybe you could have then bloodied on a hit like that, requiring another to go down, with twice that taking them out completely.Also considering various minion fixes - I don't like that they break so many rules.
Mages can use Tomes without a feat.
You don't need to houserule for this. Mordenkainen's Magnificent Emporium (the first source published that included Tomes after the existence of wizard subclasses) explicitly states all wizards are proficient with Tomes.
Some (misguided) people insist this doesn't actually give the other wizard subclasses proficiency since none of the following books mention it, but they're all published with the assumption that all you have is the PHB1 or Heroes of the Fallen Lands/Forgotten Kingdoms. Either that or because it was never updated to be so in the Compendium, but I can find a half dozen compendium things that contradict published content/errata so the compendium isn't 100% accurate either.
Not only is it not updated in the compendium but the character builder will not let you use a Tome as an implement if you are playing a mage.
Why would you want to go back to fixed healing instead of proportional healing? Healing that is proportional to the target's total makes a lot more sense.
in my eyes the character builder is terrible. I never use it for my characters