We have 3 children, every one of which was planned for and wanted... and they are still are our #1 priority. When we had our children, we never thought of asking someone else to raise them or to help us raise our kids. My parents live close by, and on the rare occasion I needed a sitter to run an errand, then they would would watch them for an hour or two... but I can count on one hand the number of times that happened. You find pieces of personal time, but you make the decision, adopt the mindset that when you have children, they are what you want to do with your personal time, they are how you spend your time, your money, your energy and efforts... with them, for them, on them.
I had my 3 kids within a 5 yr span of time, so mine are closer in age than your's will be, oldest to the youngest. Noise is a fact of life, but there is a time and a place for it. Outside voices are for outside. Normal conversations and asking how you are, how was your day, reading out loud at least 30 minutes a day for each of your older kids is a must. Your oldest children will be in school, leaving you with some one on one time with your baby/toddler. You don't mention if you work outside the home, but if you do, the drive/ride to and from work is a bit of peace and quiet that you will have. You don't mention what your husband/partner will be doing with you. Share the household chores, the feedings and bath times. Help with the homework. You make the personal time for yourself, but it's not going to be days or nights of it, again pieces strung together.
Life isn't any noiser with 3 than it is with 2. My personal time was still the same, it's how you choose to use your time that matters, I chose to spend it with my kids and my husband. If you're expecting your Mom to help out a lot, be prepared, ready for the day when she won't be there. You never can tell what might happen and you'll have to do it all. Become self-reliant, so you can teach your kids that, step by step as they grow and prosper. Give them wings.
This new addition to your family is a blessing, a gift. Enjoy!