OP. I had my LO last year and I know the prospect of birth can be terrifying, but try and remain as calm as you can.
I can only talk from my own experience, which was that my labour was very quick. Yes, the pain was horrendous, but I didn't have time to take any pain relief, and from what I've heard and read, there is a big range of pain relief you can choose from (water birth, TENS machines, epidurals etc etc), so whilst the very lucky few might have a painless labour, if you are in pain, the midwives and doctors can help.
Regarding the head of the baby being out first and staying there for a little while, for me it was a very short space of time. Head came out, two more pushes and she was out completely. When you're actually in the process of it all you won't care, you'll just want to get the baby out!
Nakedness when giving birth is completely your choice; my LO was already crowning when I got to the hospital so I was wheeled into the room, my husband stripped me off, I climbed onto the bed and 20 minutes later my baby was here. I am quite shy when it comes to nakedness, but in those moments of active labour, I genuinely didn't give a fig that I was naked. The only people that were there were me, my DH and the midwives. I promise you that you won't care when you're in active labour, everyone there is either a loved one or a medical professional, but it is entirely your choice so please try not to worry!
Once your baby is out you probably won't even notice the umbilical cord; I didn't, I was too busy looking at the baby I had just made!
For breastfeeding, this can be a difficult one. There is a huge pressure to breastfeed I won't lie, and hospitals/midwives do very much push it. Some women find it easy, some don't, and some don't want to at all. Whatever category you fall into, as long as you are happy and your baby is fed that's all that matters. I intended I breastfeed but found that I couldn't (latching and tongue tie issues), and whilst I had one Midwife who made me feel awful for not breastfeeding my baby, I also had one very kind Midwife who was very understanding and showed me how to bottle feed her and told me it was ok to not breastfeed, it has no reflection on you as a mother. And she was right. If you don't want to breastfeed, don't, and remain firm in your conviction.
Most of all though, try not to worry because whilst everyone says this, it is true that your body guides you and instinctively does what it needs to. Giving birth for the first time is scary, but it's also amazing, you'll get your baby at the end of it and if you hold onto that thought it'll see you through the labour. Hope it all goes well OP Xx