Getting back into salt water with a Nano reef

[BigMike80]

It’s been a long time since I’ve had a SW tank and I’m looking to get back into it. My last tank had a diy sump with everything hidden below. For this setup I am limited on space and having a sump won’t be an option. 
 

I'm thinking of going with an AIO. I REALLY like the look of a rimless tank with no top and I’m thinking of going with the IM 20 or 25 lagoon. 
 

Ive got a few questions about these AIOs. 
 

1. Can I fit a skimmer in the back that will be out of sight?

 

2.  Is it possible to put a refugium in the back?

 

3.  Is there a difference between these 2 besides size?

[ReefGoat]

1. It won't be completely out of sight. But they make some pretty small ones. 

2. Yes ive seem people do this. But you'll have to research on how to execute.

3. Just dimensions and 5 more gallons to my knowledge.