"But I have no idea whether my fears are justified and I want to know if a) it's acceptable to tell everyone who doesn't have a medical degree to piss off out of my space and b) does it really hurt that bad? "
Yes to number one, and for a lot of women - unless they are incredibly lucky or don't have effective pain relief, yes to number 2.
Having given birth on a few occasions I don't think you are a wuss - exactly the opposite. You are being cautious and quite right.
It is natural for people who have had good experiences with homebirths or doulas or hypnobirthing to post positive messages and it is kind of them and well intentioned. I just have an uneasiness about it. You can't control childbirth and you can't be certain your experience will be the same.
Yes, plan for an 'active birth' but it might get horribly painful so don't be put off by the scaremongering about epidurals and caesareans. If you would rather they went for an earlier caesarean if things go pear shaped rather than hang on for several days in labour, make sure that's in your notes and it is good to have an advocate and pre plan what you want.
Personal tip - if you develop any complications during pregnancy and get jollied along with 'we've had thousands of women with xyz (12lb baby lying horizontally in a wooden deckchair) who gave birth with no problems' don't believe them. Go and have a consultation with a private obstetrician outside the NHS to get the full low down on exactly what your risks are. IMO the NHS is interested in getting its caesarean section rate down rather more than protecting your pelvic floor from serious injury.
As for partner, what about having him there for labour but pop out for the birth?
Good luck and I hope I haven't made you more worried. I just think it is better to go in thinking well, it might go wrong, but I have plan B. Hopefully it then shouldn't be traumatic. But remember, for over 60% of women it is perfectly straightforward.