Trl, Its been more than a week since your post - how did things work out?
Advice? It's been a number of years since I had a casual sexual encounter, but I had a lot of them, and 95% of them were positive, good experiences. I wasn't into quickies, so almost all involved the prospect of spending a night with someone, which is different than the 20 minute hookup of today. And yeah, diseases are out there, and you will probably catch something eventually, but there is a cure for everything except AIDS and hepatitis.
AIDS and hepatitis - prevent by using condoms for anal (And you can get vaccinated to prevent hepatitis A and hepatitis B. B is the more deadly of the two, and contracted through anal sex. There is no vaccine to prevent hepatitis C).
Herpes, syphilis, gonorrhea, genital warts, crabs, and scabies - no way to prevent (You won't get syphilis or gonorrhea if you limit yourself to jacking off). You're in Korea? Less likely to get STDs if you stick to economically well off partners, who will have gotten treated right away if they contracted one. Avoid lowclass prostitutes.
If you're really paranoid about getting syphilis or gonorrhea, you could prevent it by taking a course of penicillin after your hookup, although most doctors would not recommend doing that.