I did it/am doing it alone from scratch. It's knackering but fab.
Ditto the above. Don't look too far forward, you've a way to go before the baby starts asking where Daddy is.
New relationships figure themselves out. But the person you're with has to understand that the child is always going to come first. That can be a tough ask of someone who doesn't feel the child is theirs. But it can be done - it's just a tougher hunt than usual.
Do you know other single parents? Make yourself busy and stay that way. Life goes on, and it goes on a lot quicker and happier if you're not alone.
A routine helped me no end. I knew where I was each day. Not everyone's cup of tea I know, but kept me sane-ish.
And a plan helped too. I had/have a 5 year plan that covers what I am going to do with my time (SAHM, Student, Working etc.), what DD is going to do with her time (kindergarten, home, etc.) how I am going to finance it, and what I intend to do if the sky falls. I look at it every now and then and tweak it about.
The what to do if the sky falls bit helps me get to sleep at night. Use this time now to make sure the boring stuff like your insurance, your savings etc are sorted. It's not something you want to sort with a newborn in tow. And definitely not something you want to have gone arse up when you need it.
But don't get yourself in a state now about what you're going to say when he/she is 3,4,5,6... You'll figure it out, and besides, you don't know what the circumstances will be then anyway. Best line I heard though was "Sometimes adults do things that are difficult to understand, but it doesn't mean that in their own way they don't love you" - was being said to an 8yr old, so a fair way off for you yet!