Well, firstly I would like to say that the fact that you are worrying about how you are going to be with your baby and what to do, shows that you care and I'm sure you'll be a great mum. At least you're being realistic.
I think all first timers go through this phase - I certainly did. I didn't grow up with my mum so I was really worried that I wouldn't know how to be a mum as well as what you wrote above. I can assure you it just comes to you naturally.
It's certainly a shock to the system with your first and it takes time to get used to having to put someone else before any decision you make - even little ones. Like, what time would be best to go shopping. And it takes a while to get used to your house being like a hurricane of baby stuff, going out anywhere is like a military operation with a new baby, and the tiredness can be an absolute test of any marriage!
Every baby is different and likes to be held, sleep, fed in different ways, but you will know your baby best within a couple of days and it will stay that way forever.
However, all babies are magical and so special all the tiredness, mess and lack of time to do anything like you used to are all worth it. Don't worry too much about when baby is here, enjoy the time you have as a couple now and pamper yourself rotten. I promise you, you'll be lucky to find the time to paint your toenails after the baby is born - you'll be grateful to go out with matching socks on - so make the most of your time now.
All the best
x