Chiller, Most of the time sits outside your tank so it can draw in fresh air, inside the cabinet it'll get to hot. So you sit the chiller next to your tank and drill 2 holes for the hoses.
I dont know how hot it gets where you live, But if your planning on having MH
with a hood (even with vents) and having a full reef then i'd say you need a chiller. I got mine off ebay for $187 Aussie dollars, Rated to 600L. Perfect for my tank. (4x2x2). Have a look around, its not like you have to rush and go get one. They're other ways to go about it, you could add fans blowing the surface of the DT. Also add RO
ice blocks into you sump. But a chiller is a non worry item. Will not have to worry about temp fluctuating.
My tank is open hood, And still temp rised 2c at the end of the MH
As for the hoses, I think run hoses in your sump to PVC
piping done right looks neat and good. Tubing looks not as neat i dont think.