1) What are the odds of contracting any form of STI from this situation?
Very low. Oral sex is lower risk than vaginal or anal, and performing oral sex on a vagina is lower risk than performing oral on a penis, as there isn't anything physically in your throat.
Given that it was less than 30 seconds, and that most experts don't think that one act of oral sex warrants testing, the odds are very low.
2) should I get tested?
You can if it will ease your mind, but there's no need for it. Ask for an oral swab for gonorrhea and chlamydia. This is for peace of mind only, not because you have a real risk.
3) Assumimg worst case scenario I have an oral STI, can this be transmitted to another sexual partner via penetration (penis to vagina), or can it only be transmitted by performing oral sex on the partner?
No, the only way you'd transmit an oral STI is by giving someone oral sex.