To your questions, one by one.
"I am unsure why oral sex can be considered safe if oral herpes is so common." Nobody said oral sex is risk free, and "safe" is relative. Oral sex carries some risk, but for STDs in general it is much safer than vaginal or anal sex.
1) Half the US adult population has had HSV-1 and most such infections are oral, but at any point in time the proportion of the population having an outbreak--with or without symptoms--is very much lower. As a guess, I might say one person in 1000, but no data exist and nobody knows the true answer. You are correct that avoiding oral sex with someone with a sore on or near the mouth is an important strategy to prevent genital HSV-1.
2) You answered yourself in the previous question. It is correct "that oral herpes is almost exclusively found outside of the mouth, on or around the lips". (Technically, that applies only to recurrent oral herpes. The initial infection often includes sores inside the mouth, often with severe sore throat as well.) Sores inside the lips usually are not herpes.
3) Usually the transmission risk is low in the circumstance you describe. But "near zero" might be stating it too strongly. There are too many unknown factors that can influence it. For example, if the insertive partner has had HSV-1 (oral or anywhere else), he is immune or at least highly resistant to a new infection.
4) Symptomatic recurrences are much less frequent for genital HSV-1 than HSV-2. About 40% of those with HSV-1 have no recurrences; another 40-50% have 1-2 recurrent outbreaks over the next 1-2 years, then nothing; and only a few percent have ongoing outbreaks. Asymptomatic viral shedding has been less well studied but likely also is less frequent than for genital HSV-2. (But even HSV-2 typically doesn't cause "lifelong" outbreaks.)
Regards-- HHH, MD
I’ve searched the web and this is really a unique resource. Thank you for your time and patience. I’ve tried to format these questions so that they may be useful to other viewers. I have another issue that is more personal and specific. It involves another STD, however, so I’ve posted a new question.