Did you download and install the Genesis Essentials package?
That’s the basic content pack with the Genesis base figure and some basic characters for it.
And no, you don’t HAVE to buy other characters. You can ‘roll your own’, but the included morph packs are somewhat limited in scope. There are literally hundreds of freebies available, though.
Those are probably the two most reliable/widest variety sites for content. Both require registration before downloading. Look specifically for Genesis content.