You'll have to keep generating new systems - depending on what kind of race you want to play, this may take a while until a suitable system and planet show up.
What you should keep in mind is that you can create a colony on the planet (for the spacemaster race) and terraform it to your designs - so gases are no reason for a planet to be unsuitable. What can't be changed is its gravity, and the homeworld's gravity will be the default for the generated race (although this can still be changed someplace else).
You can (and probably, should) either push the button 'HW Minerals' or 'Specify Minerals' button in F9, too. The first will change the body's minerals to starting deposits, the latter lets you specify any resources.
Once you've created a system and suitable planet, just click the 'Create Empire' button, make sure the 'is NPR' checkbox is unchecked and the rest is pretty straight forward.