Brace yourself for a tornado hitting your life
They have almost unlimited energy and are super crazy.
My parents got one last fall and it has been very stressing for the cats especially on the senior little goddess (17years old)
But they sent him to a professional trainer so things are better now.
Jack Russells are adorable and awesome dogs.
I really won't add anything as advice since great advice has been given already. Just telling a little story of a super crazy Jack Russell named Alfie heh
Good luck and many years of happiness with your puppy