The best way not to waste dollars is to join a homeschool group in your area and borrow different curriculum to go over. Or, if you are lucky and have a homeschool resale store near you, then you could view the curriculum there.
Now picking curriculum is a hot potato, inasmuch as everyone has their favorite. Look past favorites and choose based on your children's needs. Your kiddos are a little young yet but you could begin looking at preschool curriculum.
Another way to narrow your choices is to develop a mission statement for what you want to accomplish in your homeschool. Such as, I would like to make God the priority in our homeschool and all curriculum will center around Him. Or, I would like to create a classical education plan that will give my children the best possible basis for their future career paths. It's what you want to do to help your children reach their goals academically, spiritually, etc.
Once you have your mission statement then you could look for curriculum that satisfies those goals. You can also look at guideline books, such as SWB TWTM for guidance on what subjects by year.
Another option besides buying premade curriculum is to make your own out of library books, free printables, flashcards, etc. Don't discard the idea of lots of kinesthetic learning through play too especially in the younger years.
If a group or store is not nearby, start with your library. TWTM and many Pinterest sites have oodles of books for children at all grade groups for various subjects. I first picked the library's copy of TWTM before I bought my own. I have also read books on Kindle Unlimited for homeschooling and children's education. There are many blogs of people homeschooling children of all ages too.
Now here is the caveat, even after all the careful planning be prepared to have to shelve part or all when life throws you a curve. If you have been on the forum long enough you will see Mom's and Dad's trying to figure out curriculum switches, modifications, and such. Homeschool is about fitting school to the individual and this is very difficult sometimes.
So I would educate myself on the main ways math is taught, i.e. conceptual and incremental for example. This information will be valuable when your kiddos are older and you understand a little about them and how they learn. Match their learning style to the math curriculum.
Read, read, and read to them. All kinds of books, every day. Special reading time in a big bean bag chair, special time in Mommy's bed. The point here is to make it special. Start with a preschool book list and the library. CRAWL, CRAWL, CRAWL that wires the brain for reading.
In a little bit
Writing, start with tracing, fingers in pudding, etc. Make sure they do LOTS of coloring because it builds skills for penmanship.
Good luck with your adventure. I understand the need to plan (I do too) but enjoy those little ones now because it will be here sooner than you think.