All of the rules are actually freely and officially available online here https://2e.aonprd.com/Rules.aspx including every monster officially released, usually with a picture. You’d probably be better off buying at least the core rulebooks to actually read, though.
Also, Dawn of the Frogs only has 4 pregenerated characters, so if you have more friends than that it might get a little complicated.
So to actually answer your question, it depends on how much work you want to do and what your definition of “official materials” is.
All of the rules are actually freely and officially available online here https://2e.aonprd.com/Rules.aspx including every monster officially released, usually with a picture. You’d probably be better off buying at least the core rulebooks to actually read, though.
Also, Dawn of the Frogs only has 4 pregenerated characters, so if you have more friends than that it might get a little complicated.
So to actually answer your question, it depends on how much work you want to do and what your definition of “official materials” is.