Well, ill start with what i like about this idea. I love the style of mage you are suggesting, the defensive aspect especially, however I don't think it will balance mages, I think it will remove anyone ever using them in the game.
Lets go over the spells.
Golem - In my opinion, useless, you'd have to make the Golem have similar stats to a dragon to even make it worth using, and if that was done, people would scream that its Overpowered.
Orb of Healing - Not a bad one, but again, I see people complaining about this one, it would also make the Shaman useless. But aside from that, i suppose the limit on how many spells one can cast in a fight would balance that a lot.
Windstorm - I like this spell, but I am not sure how useful it would be in PvP. Im yet to see anyone use archers. Perhaps a defensive siege spell?
Transmute Rock - I'm on the fence about this one, it seems like a waste of a spell to me unless you are defending, but I suppose in certain situations it could be helpful, like if you had no other way to break the enemy wall due to your siege engines dying.
Energize - Not a bad one, but if it only works for the wizard, his offensive spells and other stamina using abilities better be worth the spell point.
Polymorph self - Not a bad spell, but the effect would have to be on a 1-2 min timer. with a pretty long CD.
Polymorph - All I can say, is no, just no. Back in the day I thought spells like this were cool, but it has absolutely no place in a RTS game. No one should be able to turn someones strongest unit / units into a flock of chickens.
Flight - Don't really see a use unless wizards are going to be awesome in melee.
Dominate - Not bad, but it would need a pretty long cooldown to make it balanced.
I'm not in any way trying to knock your idea, or tell you that it wont happen, only the Devs can say what they will add / not add. But I think this style of mage would simply make them useless. The slots they take up would not make them worth using in my opinion.
In all honesty there is a more simple way of making Mages balanced. Limit players to 1 of each type of wizard. And only allow said wizards to "pick" two spells to use. And make the only way to respec spells is to bring them to the magic guild and pay 5 crowns.
But, like I said this is just my opinion, I am sure there are some who would prefer this system.