Ooooooooooooooooohhhhhhhhhhhhhhhhh
Yes, I felt the same. I was horribly anxious for all the reasons you give.
What helped me was making sure I had told the midwife (who in turn contacted the HV system to check on me), so I knew there was a safety net this time. I also had a very frank discussion with my DH (who was surprisingly unsupportive the first time around) and made sure he knew what I felt I needed to get through it.
The most difficult time was when I had both children on my own. A feeding box (shoe box full of very small treats) for my son was a life saver: every time I simply had to sit down and feed the baby, when he wanted to do something else, I would let him have something 'from the box'. It kept him well behaved as we built up to the time, plus it occupied him whilst I fed the baby.
Re sleeping: I prioritised my sleep, so co-slept with DD and didn't bother attempting to introduce any kind of formal sleeping arrangement. I got very anxious about that stuff with DS, so threw it all out of the window the second time around. It means that she's still co-sleeping now, but it meant Iw as having at least 6 hours a night in the first months. I also didn't bother changing nappies overnight unless they were dirty. Wet ones stayed on until the morning.
We also went out for a lot of walks in the day. the baby slept (sometimes ...) and DS could run around.
Divided my time into hours, when it was getting really difficult. So if I got through an hour without shouting or crying, I felt good. Then looked to the next hour.
Make sure someone gives you quality time with the older one! It's too easy for them to give you the baby to have and take the toddler.