I agree that you should talk to a professional, especially given the long time frame. Here are some general principles.
The general rule is that you report your startup expenses in the first year you are actively engaged in the business, even if you don't make a profit in that first year. Your expenses can sometimes be deducted in the first year, and sometimes must be spread out over 15 years, and sometimes are mixed between immediate and amortized deductions.
You can be actively engaged in business without actually having a DBA, a business license, or an LLC. Those things are matters of state law and don't affect whether or not you are actively engaged in business activities for federal tax reporting.
You can also be actively engaged in business even if you don't make a single dollar. For example, if you began active and ongoing business activities in September 2021 (breeding your cats) you would not have income until you sold the kittens in 2022, but you would have lots of business expenses, and so you would report your business starting in 2021. All your expenses with no income would make a loss, that you can deduct against other income (with limits).
If audited, you might have an issue with expenses for a cat purchased 3 years ago for breeding but not actually bred for 3 years. Questions could be asked about whether you really had a business purpose at the time. You can't deduct expenses for hobbies. The IRS has a 9-factor test for whether an activity is a business or a hobby.
https://www.irs.gov/newsroom/earning-side-income-is-it-a-hobby-or-a-business
