Biminins need ballasts. M81 for the 150W and M80 for the 250W. I would not do the 250W unless you want to crank it up to 11. The Hamiltons are nice and have nice long cords. The hum a bit (about like a return pump) and can get warm, but you can mount them remotely - I keep mine in the stand since I need the heat and I cannot hear them.
I use 14K Phoenix and 20K Radiums (different tanks) without T5s. I just turn them on/off with light timers. I have nothing against T5s along with MH, but I just would rather burn another MH rather than have the same wattage in T5s. If you want to abandon the T5s for just Haildes, then you will need reflectors that spread better, but this is a bigger jump than what you are doing. Personally, I would use MH and T5 for now and see how that goes and if you feel like jumping up to 2x250W MH on larger reflectors some day, then you will have a good bit of experience and will know what to expect.
The ballasts will put out a bit of heat. The bulbs will put out more. The heat is TOTALLY easy to mitigate, but it does need to be mitigated or you can get in trouble. Just build in some fans into your DIY setup. Here in Colorado, I welcome the heat all but for about three weeks in July when I need to keep my stand doors open - nothing else. If we run the air (which is not often since it gets down into the 50s most night and the attic fan will keep the house cool most of the day), then I don't even need to do keep the doors open. In Missouri where it was high 70s at night with 80+% humidity, it was about three months and I had to use fans and keep the stand doors open. The rest of the time, the heaters work less and the heat is a blessing. I have no idea how this will do in Vegas, which is one reason that I suggested the 150W over the 250W since they make less heat. With the T5s you might only need to run the MH 4-5 hours a day so that will help too. If you turn a fan on as soon as the MH come on, they usually stay plenty cool - if you wait until they get hot, then the cooling can lag.
I was able to keep 30G breeders cool with 400W MH over them with just fans, so you should have no problem with more volume and less wattage.