Hard to go wrong with a 9mm, but if looking to familiarize with firearms and gun safety just go with a bolt action rifle, even 22LR makes for good training. That's what I learned on.
That depends. What classification? Pistol, rifle, or shotgun? For a pistol, my first was a SCCY CPX-2. My first rifle was a Del-Ton AR-15. My first shotgun was a Mossberg 500.
Home defense a pistol and depending on how many break-ins in your area a shotgun. Against tyranny the best weapon is a vote or a sign. Tanks were designed to shrug off basically anything thrown at them