Question: When Baby helps Penny out by dancing with Johnny at the Sheldrake hotel, it is stated that it is Thursday night (when Penny has the abortion). At breakfast the next day Baby's dad says they are leaving tomorrow, even though they are paid up til Sunday. Thursday night is the first night that Baby and Johnny sleep together, yet they seem to be seeing each other for ages before Johnny even gets sacked, let alone the time that's past when he comes back. I don't see how all of this be squeezed into 2 days?
Answer: They were there for 3 weeks, so they had been together for at least 2 weeks.
Question: When Johnny takes Baby up to do the final dance, Baby's dad is obviously pretty angry about it and tries to stop him. However, after the dance all is forgiven? All just from the magic of their beautiful dancing?
Answer: It would be improper to cause a scene, plus Robbie admitted to getting Penny pregnant and insulting her, especially it's what made get an abortion and medical complications.
Answer: While he probably was still angry with Johnny for sleeping with Baby, he can see how hard she must have worked to dance so well. Anger is often hard to release. Being a loving father, he is proud of Baby "in the moment" and was more disappointed with her than mad. He likely also grudgingly admires Johnny for having the courage to stand up for her.
Question: Was Baby a virgin before she was with Johnny?
Question: Despite it being pretty clear Penny had an illegal abortion the word is never said in the whole film. Was that still taboo in the 80s? Or is it more indicative of how people in the 60s didn't want to use the word directly?
Answer: I think it's both reasons. Abortion has always been a controversial topic, so the movie apparently preferred to avoid the word. In that time period, abortion was still strictly illegal, so the people around Penny would likely not say the exact word out loud to protect her and keep it as quiet as possible. It was typical to allude to something like that in a more colloquial manner, such as "getting rid of it." It's similar to how people would rarely even say "pregnant." It was always terms like "expecting," "in a delicate condition," "in a family way" etc.
Question: Baby's dad comes by to check on Penny after her botched abortion and confirms she can still have kids in the future... Wouldn't further tests have been needed to establish this? Not just a house doctor examination?
Answer: It seems unlikely that the doctor could confirm that Penny could have children without her having a complete medical exam to ensure there was no internal injury, infection, complications, etc. I think this was merely a plot device known as "suspension of disbelief." It's meant to tie up that part of the story so the audience isn't left wondering what happens to Penny. The movie can then focus back on Baby and Johnny and the rest of the story.
Answer: The father says they're leaving the next day, but when the mother asks why, he realizes he'd need to explain what happened, so he decides not to leave, and they stay for the rest of the trip as originally planned.