I just want to cry reading some of this. I was in the OP's EXACT situation. It was my FIRST baby. I just wanted peace and quiet for the first few days - was very happy for people to come and visit for an hour or less but I needed to recover, work out how to breastfeed and be a bit hormonal.
The OP is NOT BEING UNREASONABLE and some of the assumptions made about her and her attitude to and relationship with her step child are CRUEL and clearly incorrect.
I did have a 4 year old step child with me straight after I came home with my first baby. And an impossibly pushy MIL. And I remember weeping onto my tiny baby's head sitting in my bedroom alone and feeling so overwhelmed and I wanted them all to just go and leave me alone.
No-one was there for me, no-one was thinking of what I needed and yes, as a first time Mother I really did need to be someone's priority - just for a bit.
I had a very close relationship with my step child. I wanted them to be included. JUST NOT HOURS AFTER GIVING BIRTH!
When I had my second child I felt exactly the same! They came to meet the baby and then left and I had a blissful 24 hours on my own with the new baby while I recovered from labour and tried to work out breastfeeding (again).
I cannot bear the way step parents are hounded on here sometimes. I love my step child. I love my own children in a different way - and yes, more, because they are my children! If my step child lived with me full time I'd probably feel more equal but that's not the case. They live with their own Mum who they loves in a different way to the way they love me. That is ok! Pretending to be perfect step parents with perfect emotions is not helpful or healthy.
OP, I hear you. I hope all goes really well. If I were you I'd plan for not actually being home that weekend - inductions can take forever to get going and your husband needs to have plan B anyway incase you're still in labour when your step son is meant to be with you both.
Sorry for the caps and rant. But FFS people, remember what it's like to have your first baby. Even if it was a blissful, healthy and straightforward labour. It's still overwhelming and most people need a bit of time to adjust.