Ok, let's do this!
The discomfort can be really crazy, so make sure you can at least sleep. I'm using four-five pillows at the moment which I move around as I change position in the night. They really help, but you can also get fancypants pregnancy pillows which are supposed to be amazing. There are a few threads on here with details. Other than that, yoga really helped with my first pregnancy and there's a thread that has info about online videos/ classes. Swimming is also great, but, erm, we probably won't get to do that for a while 
As for miscarriage, congratulations! You're four months, and the chance of miscarriage is now tiddly! Check this out: datayze.com/miscarriage-chart
The birth is huge, but it is entirely manageable. Epidurals are the most spectacular things, if you decide you've had enough, but many people absolutely love gas and air. It made me throw up, so I abandoned it, but it was very effective. Some people swear by hypnobirthing and don't need anything at all! I imagine that your hospital aren't doing tours at the moment, but they might have a virtual one. Have a look, familiarise yourself with the the place, the sort of room you'll be in etc. It's surprisingly calming on the day to know exactly where the loo is :D Oh, and make sure your boyfriend knows where to get snacks!
As for looking after the baby, this is really, really simple, while also being really f*ing difficult. All you have to do is keep them at the right temperature, keep them fed, clean and give lots and lots of cuddles. It's simple and straightforward but the sleep deprivation and constant worry that you're not doing it right can be really, really tough. Don't ever be afraid to ask for help in those early days from the visiting midwives or health visitors. It's such a weird (and wonderful) time and it is their job to support you. There is no such thing as a stupid question. Having said that, within a day or so of the birth, there is no medical expert in the world that will know more about your baby than you. You're going to know every inch of that kid and be able to make the best decisions for him/her (sleep deprivation allowing!).
How are you doing?