You should be able to set the number of habitable worlds (and lots of other things) to your liking in the game setup menus when launching a new game (unless you go quickstart)

Perfectly normal.

The dead worlds are there to give you something to explore through. After that, they serve no real purpose.

You can't. Dead worlds serve no purpose other than making habitable worlds more special.

There are events though that may turn some dead worlds into habitable ones.

Quoting Achronous,

reply 6

Just like in real life (from what we know so far) habitable planets are quite special. Non-habitable are much more, common. You can always change the,settings

I didn't know the dead worlds included planets like mercury and jupiter. After noticing those two planets, I finally understood the intention behind the label. But I believe it's bit too hasty to label them as dead worlds because they can be used for science! Just look at all the science we got from Pluto in 2015 Ice volcanoes.

Absolutely my opinion, I wrote a while ago in another thread that I would like the possibility to make class 0 planets habitable with a lot of work or to be able to explore them for treasures or something like that, so that they serve a real purpose instead of only being fluff.