What if I underfeed her? (I'm bottle feeding)
Would you consider trying to breastfeed at all? I don't know your reasons for not planning to but I really did find this aspect invaluable - breastmilk you can give any time, as much as they like, for nutrition as well as just comfort, and you never have to worry about giving too much or too little as baby automatically takes what they need. I definitely would find this more stressful to get right with formula, and you need to find other ways to soothe baby when they need calming in between feeds (whereas with BF you can just offer boob each time).
How do I take a newborn on a walk?!
You just have to dare to try once, say just down the road and back to start with! And then you slowly get used to it. Pack a bag with nappies, wipes, muslin cloths, change of clothes, and whatever you need to feed them. Change and feed baby (potentially then change again and then feed again etc
). Put a hat on baby, plus adequate amount of outer layer clothes. Either pop into sling (sling counts as one layer) or in the pram and you get a feel over time for how long they're happy in either. Once they're no longer happy, take them out and feed/rock them! 
What if I dress her wrong and she's too warm/cold?
I stressed about this too at the beginning but you will soon get a feel for it trust me! Imo you can't go wrong in the beginning with long sleeved vest plus sleepsuit. Plus hat for the first few days; plus cardigan/coat and booties if out with the sling; alternatively plus coat and blanket if out with the pram (I know snowsuits very popular but with those you do have to worry more about overheating. You'd have to take them out of it when going inside somewhere, which you won't want to do if they're just asleep! Whereas a blanket you can just remove.)
What if she doesn't put on enough weight?
You will have your health visitor to talk to in case there's any issues, and the midwives come around too in the early days to check!
When can I stop supporting her head?
She will start to lift it herself at some point so you will be able to tell when she is developing more neck strength
When can babies go in a pool?
My considerations would be (1) how easy or tricky is it to keep them warm - unless you have access to a therapeutic pool the water will be much colder than what is advised for baby baths. I'd want them to have gained some fat around their body first. (2) Pool cleanliness- perhaps wait until after first jabs
When can they sleep on their stomach?
Once they're rolling themselves into that position. You always put them down on their back, likely at some point she will then roll herself onto her tummy or side - then it is okay to leave her like this.
What do I do if I wake up and she's on her stomach or side?! Is that fine?
Yes, fine 
I know how you feel!!! I was the same! But don't underestimate your motherly instincts- they're not just magically there the minute she is born, but they develop over the first few weeks just from how much time you spend with your baby. You will soon be able to read her cues and get a feel for what she needs! All the best OP 