Can precum on vaginal opening transmit sti like chlamydia/gonnorhea etc. can it travel into inside vagina and to upper reproductive system?

Sure but less likely: That's why we do routine testing of sexually active (any activities) patients at annual visits. Couples who are not monogamous can easily add outside STD germs to their relationship. A larger number of germs makes it easier to set up an infection, but many things are possible in life, meaning a small number of germs still can start an infection. Avoid STD germs by verifying partners are germ-free.