you can use a normal mh bulb in a hps ballast without hurting the ballast @ all.
It makes the mh bulb blow out in about 3 months of use but thats all youll need out of it to veg with anyways. That could actually do a couple grows.
The reason the bulb blows faster is because there is 1 extra part in a hps ballast that isnt in an mh ballast called an igniter. Since your thinking of getting a 150watt hps, they dont make name brand mh bulbs that small anyways, youll be using cheapos that cost about $10.
That Would works LOTS better than that T5 setup bro. Believe me Ive used both before. I was told that fluro tubes were okay to go with and would do well but they produced loose fluffy airy buds that didnt weigh much of shit, althogh as potent as any other. When I made the change to hps my yields went up by 3x wile still being potent as fuck.
You can actually get a good 400watt hps ballast for about $80 on the internet though....not sure why your wanting to go with one that small as 150watt.
If you ever decide to aircool it, Diy a cooltube for it only costs about $60.
Ive used a 400watt just fine in a 4x5 area before with no cooling though.