I'm guessing I couldn't do LDR unless there was a lot of communication, or it had already been a local relationship. Previous posters have asked good questions - just what would make you feel like you could know him enough to be comfortable? If you think it is too good to be true, is there a way to do a easy background check on somebody not local? (If he is a Doctor, there should be SOME searchable information on him (admit I'm having trouble myself finding that info for Brazilian Dr's), I tend to get suspicious so I would probably seek it out and look for inconsistencies before he was back in town, if anything looked fishy I wouldn't roll the dice.)
As for safe sex - well if I couldn't trust my ex-husband of 12 years, I figure I can't trust anybody. Condoms for sex and oral sex is my routine for non long term relationships, and as awesome as it is, I don't mind forgoing oral sex until I feel I've known somebody long enough time to get a sense of who they are and what other relationships they are in, whether that's 6 months or never. There is nothing wrong with erring on the side of caution, and anybody worth having a relationship with wont be pissy you wont throw caution and common sense to the wind.
I too think if I had a spark with somebody, was comfy with casual, and it was going to be 2-12 times a year when they were in town, I'd still feel safe enough with my current safe sex rules to stick with them and go for it.
Happiness will never come to those who fail to appreciate what they already have.