You will be fine with the pain. EVERYONE worries about the pain, even after having had a baby. You ALWAYS worry about the pain, you'd be mad not to, who wouldn't?
For me I found the pain of childbirth a productive and manageable experience. My DS took 60 hours (they would never let you go this long, I pushed for it and there were geographical issues) to be born and I had pethidine and TENS. My DD took 12 hours, I had only the TENS. I found the the pain starts small and builds slowly which helps your body to adjust and cope. If you had the intense pain of the final stage of contractions at the beginning I don't think you'd be able to cope with it but by the time I got to that stage my body was ready and prepared to accept it and it felt exciting and productive as it was evidence of the imminent birth.
This is hard to explain but I am very glad of the labours and vaginal births I had and the pain is part of that. I want the pain this time, I need to feel it naturally as much as I can and I am confident that there will be methods of relieving it if it becomes unmanageable. That is the trick I think. If you let it do it itself so it builds and make sure you ask when you want pain relief then it is a good experience (to me anyway).
I would have a frank discussion with the consultant about how to balance your peace of mind and needs in labour with what is actually necessary to look after your babies. If you want to be able to move see if they will let you move and be monitored e.t.c
Having a good midwife and pushing at the right times helps to prevent tearing or needing to be cut. It is unlikely you will be out of control. My experience was that you become a bit insular and everybody around seems a bit further away than they really are which makes you feel very in control. Put in your notes that you want people to discuss things with you before they do them if you are worried (or something nice that means that ) Put in your notes that you would like specific guidance about when and how to push to avoid tearing and that you only want to be cut as a last resort. Basically anything that is important, tell DH and put it in your notes.
I can see why you'd be tempted to stick with the original plan to section but your sound like you want to give vaginal delivery a go too. It's a difficult and unenviable position but the main thing you should focus on is that soon your babies will be here and none of this will matter (hopefully).
you are definintely not an idiot or pathetic and it is normal to be scared x