Why would you need MH for a 24" tank T5s are more than adequate but do not waste your money on MH if the tank was over 30" deep and you wanted to keep SPS and Clams on the sand bed then fine, MH are very old school I see more people upgrading from MH to T5 on a weekly basis for a number of reasons
1 A lot cheaper to run
2 better choice in colours
3 generate a lot less heat
4 Proven SPS growth and colour
You have made a good selection on the lights the ATI lights are far superior to may unit available and are a good price
I would be very cautious with Bubble Magus skimmers they have good write ups but I have serious reservations about support etc. I would keep my eye peeled for second hand APF 600 or even look at the MC500 Turbo
I would use 2 heaters and a heat controller like a TC-10