I think you should try to make a very general layout on a big piece of paper, choose one part of that world and maybe narrow it down to a piece of your world as large as... well, the middle parts of Europe or maybe half of USA. Start out with that, make a map over the area and start making maps of the surrounding areas and so on.
To make a world as large as Jupiter is a humongous load of work if you want it detailed. If you want all of your stuff in one map, and you also want it to be detailed you need some kind of super computer - otherwise "normal" big mountains won't even show on you map, in comparison to the titan-cities or thousand-dragon-mountains.

I'm making a map that is probably as large as one fifth of, say, italy or sweden - the size of it is 158 meg and it's not even very detailed.

So my suggestion and advice is:
1. General layout
2. Choose an area
3. Map the hell out of it!
5. Repeat - and use each map in conjunction with the others to describe epic awesome adventures.

Believe me, you'll want to add a thousand things and you'll want the possibilities to change and add lot's of stuff - starting out small in a big world is not wrong.

I definitely want to see this happen! I love huge worlds - but also consider the details in everything, every culture, every people, every creature - how do they get along or DON'T get along, what about war, what about magic and nature? Has the world changed over time, is there still unexplored areas (there should be in a world as large as yours!)?