I think some nerves are to be expected as you approach your first birth, after all, you've never done it before and you don't really know what it's like, so no matter how prepared you are you still feel uncertain etc.
Having a homebirth can be a wonderful experience. Mine was utterly fabulous, calm, relaxed, easy, euphoric.
I'll tick off the points that you are concerned about and try to ease your mind.
"the baby does not breathe on its own after it is born,"
When a baby is first born it is still recieving oxygen from the placenta via the umbilical cord, so if the cord is left intact and not clamped and cut the baby has time to start breathing slowly and gentley. As long as the cord is intact and the placenta is still attached the baby is not being starved of oxygen. In the event of your baby having actual breathing difficulties at birth then the midwives attending will be fully trained in neo-natal resus and (as far as I know) all homebirth kits include a full resus kit including masks, oxygen and so on. So, if, when your baby is born, be you at home or in hospital, don't panic if s/he doesn't instantly let rip with a lusty wail, but starts breathing slighlty slower. This is ok, as long as the cord is intact and hasn't been clamped. (I'd make the midwives repeat it like a mantra, "the cord is not to be clamped until it as stopped pulsating, the cord is not to be clamped until it has stopped pulsating....")
"that another serious complication arises that could be treated successfully in hospital but not at home"
Like what exactly? That you'll start to bleed massively? The midwives will know how to handle that and will give you iv fluids and syntocin injections whilst blue-lighting you to the nearest hospital. I can't think of anything else that is likely to be catastrophic, that would be a sudden event that could be dealt with in a hospital but not by the midwives in your home.
Sure, crash c-sections happen, but they are very rare, most emergency c-sections are done once the theatre team has been bleeped and assembled and so on, and this takes about 20 minutes, so as long as you are no more than 20-30 minutes away from hospital then you'd get in just in time to be wheeled into theatre, rather than waiting in the delivery room for 15-20 minutes until the staff etc are ready for you.
Most birth complications have signs, (meconium in amniotic fluids or what ever) and the midwives would pick up on these signs and tell you they would like to transfer you to hospital.
Ultimately, don't panic, the midwives who will attend you will be highly trained and experienced. You are more likely to be left with a student or newly qualified midwife if you are in hospital, but this won't happen if you are at home. The best thing to do now is to go over why you wanted a homebirth in the forst place, read your Michel Odent , Shiela Kitzinger , Ina May Gaskin and Grantly Dick-Read books again and remember, if you're a healthy woman having a healthy, normal pregnancy, there is no reason to believe that anything will go wrong.
And finally, you can change your mind at any point and go to hospital, before you go into labour, in the early stages of labour, or in the full-on pushing stage, it's rarely too late to get in the car/ambulance and transfer. However, you may find that you feel fine, you are comfortable and relaxed at home and have no desire or need to go to hospital, and end up with a bliss-ful homebirth like I did. But, if you cancel your homebirth now, you can't really change your mind and decide to stay at home once you are in labour. To be a safe homebirth you need midwives in attendance and they will need thier birthing kit, some NHS trusts deliver this to your house once you are 37 weeks, it includes Gas & Air and all the drugs, resus kit etc that they might need to help you birth your baby. If you cancel your homebirth this equipment will not be readily available, so you can't really decide to stay home after all.
Discuss it with your midwife, by all means, but I'd advise you not to cancel it and to just see how you feel when things kick off!