can you combine affixes together? Like would the following words be acceptable?
Malbonulego = a big bad person
Malsekejeto = A small wet place
Fluguleto = A small flyer
yes you can. there is a part in "being colloquial in esperanto" where it talks about people combining (for humourous purposes) a rediculous amount of roots and affixes together to create these insanely long words, so there really isn't a limit on how much you can combine. you can also make words that are just combined affixes, without a word root at all.
Yes, but my sense is that the first one should be malbonegulo, and in either case would mean "an extremely bad person," as -eg- in an intensifier; it doesn't mean bad. After all, the fairly common bonega, means "great," but "big good." For this one, instead of -eg-, you might want to use -aĉ-, which means "wretched." Malbonaĉulo, a wretched bad person.
Likewise, -et- is a de-intensifier, and doesn't mean little (generally). Sure, eta means "tiny," but malseketa means "damp." So a malseketa loketo is "a small, damp space."