Fuge set up question

I was looking to start building my sump/fuge today for my 45 gal oceanic and realized the 15 gal high tank I was planning to use wasn't going to be the best option due to space. I plan to use an SWC skimmer, mag 5 return a BRS dual reactor and a small fuge. All this was getting to be too much for the 10" X 20" X 18" space in the tank and not leaving much room in the stand.

So what I decided might make things a little simpler was to switch to a 10 gal tank that is a bit shorter thus allowing myself the height to add a separate container/tank to put the refugium in.

What I came up with was to use a black plastic battery box that is 11L X 7 7/8W X 10 3/4 H. It even comes with a lid that I can open up to put the light over(with the black plastic and lid should also cut down on the extra light coming out of the sump at night). This fits perfectly to put on top of the 10 gallon tank (sideways) and will give me more more room in the sump for the skimmer/return and reactor. I plan to feed this with a T off the drain and add a bulkhead fitting with a hose on the end for it to overflow into the return in the sump.

To get to the point do you guys see any issue having this sitting on top of the 10 gal tank?

Also I'm debating going with a DSB or just adding about 2" of sand
(or maybe just leaving out the sand), a little LR and some cheato. Would there be any major benefit of adding a DSB to such a small area? Obviously I don't have alot of space to work with but want to take advantage of whatever benefits I can get out of my set up.

Any other thoughts, issues or recommendations anyone can provide? If pics are needed of anything please let me know.