Twice I've called an ambulance (once they arrived after the birth, and once they arrived in time to sprint me to the hospital with minutes to spare). =)

Personally I'd try to make it to hospital, just for the reasons Nickle stated—I love and appreciate knowing that paramedics are ready to come out and help, but they're not midwives and bless them, some can get a bit panicky (they try to hide it but when they are practically begging you to hurry and get to hospital, you know they REALLY don't want to be the ones in charge lol. And fair enough!).

So, I guess if I realised things were really happening and a car wasn't an option, I'd call an ambulance and hope to make it. The only time I wouldn't get IN the ambulance would be if I was pushing already, because it takes me about 10 minutes to do that and I'd rather birth at home than in an ambulance, and it makes no difference in terms of who is attending. Otherwise I'd hope to make it. I'd also try to be on speakerphone to a midwife, for a bit of guidance and peace of mind for everyone. If an expert can't be there, then at least having them consulting would be ace.

If the baby was already born, I think I'd still call an ambulance (if I didn't feel up to being driven), because I have no idea how I'd be able to tell if I'd torn, and I wouldn't mind being checked for blood loss, having baby checked over, etc. That's me, based on what's happened with previous births, those are things I don't think I'd feel up to monitoring and managing on my own. Maybe others would feel more confident to be independent there, but I wouldn't mind seeing a midwife I think. So, you don't HAVE to go to hospital, I'd just encourage you to consider, if you bleed, if you tear, if baby is a bit jaundiced, if you go into shock from a speedy delivery—are you resourced enough to identify that, and deal with it? I don't want to be alarmist or anything. Just have a plan, Stan.

I think the paramedics will call the hospital to tell them you're coming, so you don't necessarily have to call the hospital. I think mine called the hospital. They were on the phone to someone, lol.

I think on the birth form, they put the midwife who saw me when I got to hospital? If you didn't go to hospital (and you don't have to) I guess they wouldn't put a midwife?

As for having things on hand, your usual birth aids (for massage, relaxation, thirst, comfort), plus a few towels and a blanket. One towel to clean baby off, another to wrap baby in for warmth, and then a blanket for you both.

I've heard leave the cord (had not heard the thread thing, not hard to have thread on hand though!), but I guess if you weren't going to hospital you'd want to read up more about what you'd want to plan longer term.

There is a cheapish book (maybe free in pdf form, I'm not sure) called Emergency Childbirth, that might help you sort things in your mind as well. Just to help you identify what you are needing to consider (though with 4 kids of your own, I imagine you probably have a good idea of what to think about).

So there's my random thoughts. Based on past experience, I'd try to make it to hospital, because paramedics are not midwives. But if it all happens before you can blink, I've read that most full term babies that just come in a hurry tend to be pretty straight forward, and hopefully (with a bit of just-in-case preparation) you'll be fine. I can't imagine having the baby at home without then getting someone with a bit more expertise involved, but that's just me, and I'm sure a previous PPH and tear and shock and big babies and so on, absolutely influence that mindset. If you feel confident that you are equipped to identify any issues that might crop up and have the resources to deal with them, then it's definitely your call.