i was never a fan of the pre-built sumps because of the price, but thats my personally opinion and i see why you are going this route because it fits. i first would suggest you sit down, think real hard, think some more and then decide. what should you be thinking about? future setup, upgrades and where the tank is going to be down the road. are you keeping it? just short term? going to put it somewhere else? these are questions you should consider as it could change the way you should go about the sump.
IF you are any good with DIY, i suggest ( or atleast what i would do ) is build a cabinet next to the tank where a DIY sump ( made from a used fish tank/tub ) and shelves to put chemicals and equipment that matches the stand of the tank. this will still offer a clean look of having a sump under the tank and things will be out of the way.
another option is going to the basement or garage to put a sump ( if they are close enough and the wife approves
im just throwing ideas out there to think about so you wont get stuck buying equipment twice or getting something only to upgrade it shortly after.
your safest bet for an overflow box would be to drill the tank and you wont have to worry about power outages and so forth. i had an enclosed overflow going for some time both with and without an aqualifter pump and either way ive managed to overflow the display. dont get me wrong, overflow boxes are safe- granted they keep the water to keep the siphon going and the aqualifters make it close to 100% safe UNTIL the tubing leading to the pump clogs, which only should take a weekly or bi-weekly check up/cleaning to be sure its running properly.
as for which overflow box this is all preference in my opinion. the first one will get dirty fastest because its made of clear acylic, however the U-tubes easily slide out and will accept a flexible pipe brush as opposed to the enclosed boxes which are impossible to clean inside similiar to a drilled tanks overflow box which can also be a trick to cleaning. on my newest tank, i personally went with a kit from www.glass-holes.com
where i got an overflow rated 1500 gallons and it is the smallest in tank overflow box ive seen yet so that may be another option. make sure your not drilling tempered glass, ever.
what confuses me is that you want to put 1'' substrate in between the baffles? what does this do? am i missing/misunderstanding something?
the hang on refugiums prob. wouldnt hurt but at the same time dont know how much good it will be doing. i would add one of these to tanks less then 30 gallons. it may be pretty sweet to tie a 5 or 10 gallon tank into the sump and have it displaying your refuge next to your display tank, the overflow could drain into the refuge tank, then into the sump and then pump back up to the display. just another option. ultimately im a fan of a DIY sump that includes a section for refugium purposes.