There's enough empty space in our solar system to fit every star in the galaxy within its volume

120 AU diameter gives you over 200 billion Sun's worth of volume, but 160 AU diameter gives you 5 trillion. However, definitions of the solar system's diameter can be up to several 10,000s AU(!)

Even on the lower end of definitions on the solar system's size this works. There are 0.2 trillion stars in our galaxy: for a 400 AU diameter solar system you'd fit 80 trillion Suns of volume. At 1000 AU diameter = 1,250 trillion. 200 AU diameter should be more than enough tho.