Regarding the question of Kabolas Ol Mitzvos, one thing must be kept clear: It is kabolas Ol Mitzvos, not Kabolas Kiyum Mitzvos. The requirement is that the ger must accept the obligation to keep the mitzvos; he is not required to commit to actually keeping them. The gemoro’s loshon in this regard is very on point: He is not told “Yesterday you could eat chelev and from now you will no longer be able to eat it”. That would make sense. But no. He is instead told “Yesterday if you ate chelev you did nothing wrong, but from now if you eat chelev you will get kores”. In other words we assume he will do averos, and he must accept that he will be punished for them. In essence a ger is saying he’d rather be in a Yiddisher Gehennom than in a Goyisher Gan Eden.
For instance, there is a teshuva in Igros Moshe about a woman who admitted, years after her giyur, that in the mikeveh, at the very moment she was telling the beis din that she accepted ol mitzvos, she intended to do an avera. She was under no illusion that it was not really an avera, she knew that she was now going to be obligated in mitzvos and should not do it, but the temptation was too strong. Reb Moshe paskened that the giyur was 100% valid. A ger does not promise to be a tzadik. Everyone including the beis din knows that he will do averos, because he is a normal human being with a yetzer hora, and giyur does not get rid of it. The fact that she knew what she was planning to do was an avera is enough to validate her giyur.