Heli - all that stuff looks perfect. I might actually switch to a 120mm rad & fan too; pretty sure my dual-fan 80mm rad doesn't have enough surface area. Turns out a 120mm single-fan rad with one fan has more surface area than an 80mm dual-fan rad (120mm * 120mm > 80mm * 160mm)! Look at that middle school geometry in action.
Anyway, to your questions:
1) Without the front nozzles, you'd just run the lines to/from the rad directly into the reservoir. The 'out' line would be hooked up to the pump, which would sit in the reservoir; the 'in' line would come directly from the rad and spill into the reservoir.
2) Get the rad barbs to match the OD (outer diameter) of the fitting on the pump. I noticed that particular model you linked doesn't list one. It's usually either 3/8" or 1/2" size. Make sure you know the size of the fitting on your pump before you buy the barbed fittings for your rad. Selecting the fitting size was easy for me... my pump comes with a 1/2" or 3/8" adapter, and the standard size of the nozzles on any water cooler is 3/8" NPT, so I just got everything in 3/8" size. Frankly it doesn't matter; just pick one and go with it, as long as all your equipment matches. I prefer 3/8"... it's smaller, and you don't really need a super-thick hose for this application.
3) The mini-fridge in the base is very cool. Not sure how powerful it is, but I'd try to make use of it. If I were you (and I had the right equipment) I'd try and put a coil of copper tubing in there to help cool the water down on its way back from the rad. You'd likely have to drill holes in the side to feed the tubing through. But the system would look like: cooler --> rad --> coil --> cooler.
One thing that might cause issues: using the setup described above, you might run up against the limit of the pump. Each pump has a "maximum lift" metric... usually 2 or 3 feet for low-powered pond pumps like this. So make sure that the pump you get is powerful enough to lift water from your cooler, up to your terrarium, then from the coil back up to the reservoir. Here's the pump I use... it's 120GPH (a little more powerful), supports 3/8" or 1/2" fittings, and it's got a good 4' maximum lift.
http://www.amazon.com/gp/product/B000VMF3N6/ref=oh_details_o01_s00_i00
Chew on that for a while! Looking forward to seeing what you do with this setup.