Your actual budget setting thing doesnt seem to do much (unless anyone can say better), but yes, for sure, in a secured main country dismantle and/or sell off as much military as you can, you will save loads of money. Military is the most expensive thing, dont have ANY in your main, not needed.
The only exception to this is: when you are making a bit of cash and ready to take on another country (slave) then you will want to get enough offensive weapons to take a C3. Get your economy going first though would be my advice.
(NB for any other new players reading, this DOESNT necessarily hold true for Fearless Blue because there are no secured mains)