So for a modeller like me, it will be hard?
If so, what programming language should I learn?
You should probably find a programmer or two for your team
Otherwise, the engine is written in C++, like most of the games out there.
So how long (in years or months) would you say it will be until it supports say, 30 star systems each with about 10 planets?
If we ever get out of our solar system with this, there will be an artificial planet generator, and it won't matter whether there are 30 or 3000 systems - we won't model them manually. However, as I said, we want to focus on our planet first, to exploit fully the potential it provides - and that is enormous. Our focus is shifted towards ground level detail, unlike say Infinity that has relatively rough ground details in comparison but focuses on the space.
How long until there's an explorable universe in Outerra - we can't say. Depends on too many factors. I guess we will be fully occupied with Earth modeling for some time, so a planet generator might come in order only in a year or two, as an experimental feature. Artificial planets could be supported even now, but the output of standard fractal noise generators applied to planets makes them quite boring.
5. Are cities procedurally generated too?
Not yet, but it's in the plan.