My kids are 5 and 3. Boy/Girl. Just over 2 years apart. The running joke in our house is that my son=3 kids in one! He can outrun the energizer bunny, is very independent (read stubborn), and once he is focused on doing something (good or bad) he will do it no matter the consequence. So I definitely had my hands full with him and still do.
When my daughter was born, we did have a lot of help for about 2 months before and 2 months after she was born. I was put on bedrest at 26 weeks. And spent about a month actually in the hospital. 2 weeks before she was born, a week after (I had a c-section) and then a week later I was back in for an emergency bowel obstruction surgery.
But after I recovered it was just me and the kids while hubby was at work during the day. I enrolled my very active son in preschool about 4 months after my daughter was born for 2 mornings a week. Hubby would drop him off at school on the way to work and I would pick him up at lunch time. That worked perfectly for us and my son loved school!
When we were at home, I would play with my son or read to him or take him out in the front or back yard to play whenever my daughter was napping. We have a pool out back so I'd swim with him or push him around the front yard in the wagon.
I made sure to take both kids outside (weather permitting) everyday. We would either walk around the block, go to the mall, or even walk by the beach. I'd bring our Bob Rebvolution Duallie stroller, snacks for my son, diaper bag, and the Maya wrap (ringsling). If my daughter got fussy in the stroller I would put her in the Maya wrap (both my kids loved being squished up in that thing). If I needed to breast feed her while were out, I would pick places that had a small enclosed play area for my son (like the mall) or indoor play places (even Mc Donald's or Carls Jr). I would use the Maya Wrap to cover me and DD up while I breastfed her and I could still keep an eye on my son.
The first official solo outing with the two kids was by far the scariest for me. Once I did it though and got over my fear, I was fine. I just did a quick trip to the grocery store down the street to pick up a prescription. I was stressed about how to unload and load both kids into the car while keeping them safe in the crowded parking lot. We have a minivan, so I would park near the grocery carts, get out of the car and lock it with both kids in it, grab a cart, and put it by my daughters side of the car. I would then go to my sons side of the car and get him out of his carseat and have him walk over to his sisters side. I'd put him into the rear of the cart and then put her into the front of the cart in her carseat. I'd do the reverse when loading them back into the car. Same thing if I was just using my stroller.
After that first outing alone, things got much easier.
Another really good thing is to do outings with a friend who has kids that are similar ages to yours. That way your kids have someone to play with and you can have some adult conversation to keep your sanity :) Try finding a meetup group near you, or enrolling both your kids in Parent and Me classes. I did an Intro Music class with both kids where the age group was from 6months to 3 years. Both kids had fun.
By the time your new baby is about 3months old, you will have your schedule set and will feel pretty comfortable going out and about with both kids in tow.