Larger Nozzle?

Decide what layer height you want to deal with then go for it.
I have used nozzles from 0.2 -> 1.6 (used a Volcano adapter on the ones larger than 0.8) and all you are losing is resolution.
Maybe your parts are big and that lost resolution doesn't matter (it generally doesn't). For routine work and test parts we run with a 1.0mm nozzle unless it is a really small part (and then 0.4 is usually fine).

Advantages to a larger nozzles are you can print a lot faster The more plastic you can push out in a single pass the faster your print is DONE.

 

Nearly anything that says it is E3D compatible will work on the default Hexagon hotend.

 

There is almost no difference in nozzles*
There are a few different types, but if you get E3D compatible nozzles they will work on the Robo just fine.
You do not have to buy them from E3D either, just make sure that they are E3D compatible.

One thing to consider is a rule of thumb I use. It is not a hard-and-fast rule, but more of a "guideline". For best results you want your layer height to be %30-60% of the nozzle diameter size. Make that adjustment in your slicer.

The standard 0.4mm nozzle with a 0.2mm layer height falls smack in the middle of that. Can you print outside that range? Absolutely. I have seen 0.05mm layers from a 0.4mm nozzle**, but you need to have the printer tuned for that to get the best results and out of the box/defaults everywhere that rule of thumb works. Start with that and then play around.

*not ALL nozzles are the same, some of the makerbots and a few others use some that are totally different.
**search the forum and you can find examples from one of our members @tesseract that show just how fine a detail you can get with a 0.4mm nozzle.