Hi,
Just came across this and though I'd sign up just to post a couple of things that I thought you might find useful.
Ive had an orca80 for a year now, its marine however, and its a decent little tank.
Firstly, if for whatever reason you've gone against using the back filter, its still a great place to "hide" things, esp your heater, which I noticed in one of the photos. No need to show that off. Also, having it in the back protects it from bumps that may crack the glass... and, well water and electricy... Of course, drip loops, surge breaker, etc shold also be use, but no need to risk it.
Secondly, I too have had fish "dissapear" in my tank. Has happend a couple times now, and always ended up finding them... yep, in the back filter. Doesnt look like there is enough room for them to go between the lid and the barrier, but, its happened to my clownfish twice now.
You did mention turning it into a marine. I'mnot sure I'd recommend this. I mean, mines been great, but from my experience, its just too small. Marine tanks need a very stable pH, and such a small tank, its hard to keep it that way. On top of that, fish like Mandarin, that feed off the critters in the live rock, owont have enought live rock to feed off, so you're really limited. You just end up pulling your hair out if you believe folks at the LFS and go ahead and buy one, and then watch it waste away no matter what you try.
That, and once you start with marine, you just want to go bigger and bigger....
Anyway, here's a couple photos of mine. I have taken the filter material out completely, and I've added a protein skimmer. Unless you happen to have a tunze nano skimmer kicking around(smallest best performing one I could find), and some spare time and a lot of patience, its possible not worth it. But, I wanted to try the berlin method, so its just the live rock, and the protein skimmer keeping things ticking over.
Best of luck,
Stu