How hard is it to have a newborn with a 18 month old

I am so scared out of no where. I’m 25 weeks and my first baby will be 18-19 weeks when this baby is born. Everyone is like goood luckkkk and telling me how hard it’s about to be. Obviously it won’t be easy and the newborn stage was realllly hard for me with her. I had ppa and I literally couldn’t sleep at all bc i was so worried about something happening to her. It took a month or 2 to get adjusted

My other problem is I finally just stopped breastfeeding my first and she’s still sleeping in bed with us. I’m planning on using a co sleeper thing that attaches to my bed for the new baby. Should I get my first into her pack in play at night before baby comes or do u think it’s okay if she stays in bed with us ? I’m so confused on how sleep schedules are going to work when new baby is here. I’m worried about not giving my first sweet baby enough attention. I’m so nervous about being a good enough mom and I feel so lost right now.

Also I am sooo scared about leaving her when I give birth. I have never left her for more than 2-3 hours.