New set-up, need advice

[Aquattro]

Couple of things to consider.

That's a smaller tank, so a 250w MH will likely introduce heat issues. How will you deal with that?
"High flow" is subjective. With a 15g sump, you're not going to pump a lot of flow using only your return pump. Other options are in-tank pumps or closed loop. With a lot of flow comes substrate concerns...are you wanting sand? Might be a storm
Clean water and proper levels of Ca/alk will give you great growth coupled with good enough lighting (250w would do it). Some people like to dose Mg, so test and see if you need it once your corals start growing.
Keeping these levels comes with options. Ca reactor, dosing pumps, kalk top-off or manual dosing. You can spend 20 bucks or 800, more money isn't better, just sometimes easier.
Evaporation with that size tank using MH will be a couple of gallons a day, how will you top-off to maintain SG. Again, you can go cheap with float valve and jugs, manually top it off everyday (gets old fast) or go with ATO.
That's just a couple of things to consider. Pretty much figure out how much you have to spend, then determine the best way to spend it.

[ReefOcean]

Cool and thx. I never even heard of a closed loop. I found an easy and cheap over-the-top design online. I think I will go with that instead of powerheads.

As for temp, I have a chiller but if I keep all of my pumps outside of the water, would that significantly help to reduce overheating? I can just draw water with my skimmer, return and reactor pumps with piping while having the pumps outside... What do you think or will it just be a big mess?

[Aquattro]

"mess" is relative, it's whatever works for you. But the light will add heat. You might get away with using fans, you might not. If you use the chiller, it could add to the heat in the room, causing a vicious cyle. I run my chiller remotely to avoid this, you may not be able to..

[intarsiabox]

Have you considered a 6-8 bulb 24" T5 fixture? You will be able to grow anything you want with less heat than MH, plus you can vary your color depending on bulb selection. I don't know much about LED fixtures but some of the new cheaper models look like they may have some merit to them.

[ReefOcean]

will 144 watts of t5 be alright? I understand that 54 watts of T5 give off 5000 lumens so a 6 bulb fixture will give off roughly 12k lumens and about 30 more efficient. Sigh, as soon as I think I have it figured out..hehe

I do like the idea though, I have problems controlling my temp with just LED over the tank. I might be adding 20 gallons with my new system, but I am starting to worry more and more about the heat of metal halides. I really thought it was negligible.

What would you suggest for bulbs ina 6 bulb fixtures? 4 10k and 2 actinics?

[Aquattro]

T5s still get hot if inside a canopy, so if LEDs are giving you temp issues, so will T5 bulbs. But, compared to MH, the issue will be a lot less. MH will give you sunburn if you're playing in the tank too long

[asylumdown]

I had 2 250 W MH bulbs over my 90 when it was running. In the winter, the ground floor would hover around 18-19 degrees and the lights alone could keep the water at a steady 24-25 during the day. In the summer we let the house heat up to 24 in the day when we're not home and I'd usually have to turn the MH off when I got home from work around 5:30 (3.5 hours early) because the tank would be pushing towards 28 degrees.

The tank had no canopy and was free-standing, so MH can definitely make a big impact on the temp of your water.