We have two large wire shelving units on our wall, in between them is a large storage cabinet type thing with doors that close - where I keep art/puzzle stuff “locked up”. Fabric boxes on the shelves with different toys and we rotate or bring down what she wants. Box for magnet tiles/blocks/cars etc. things like her little dollhouse and other favorite toys are on the bottom so she can play as needed. The rest of her toys are in her room. We have another cubby style storage in her room with the same - books/toys and Knick Knacks in fabric boxes. Also lucky enough that her bedroom has 2 small closets so one for clothes and the other for more toys. After reading this I have an urge to toss toys now XD
AmazonBasics 5-Shelf Adjustable, Heavy Duty Storage Shelving Unit (350 lbs loading capacity per shelf), Steel Organizer Wire Rack, Chrome, (36L x 14W x 72H) https://www.amazon.com/dp/B01M0A4B9M/ref=cm_sw_r_cp_api_fabc_QNOYFbAMW5MTF?_encoding=UTF8&psc=1
This book is decent.. I won't say it totally resonated but there were a few interesting points.
Maybe some of the books written specifically about having a second child would be worth a look. Here's one, and I know I've seen others.
https://www.amazon.com/Second-Baby-Book-pregnancy-firstborn/dp/0349420041