LLCs can be expensive, and usually require a lawyer ($$) to properly execute any sort of restructuring. They are primarily a tool for isolating liability, which shouldn’t be an issue for a private studio. The IRS has strict guidelines for “hobby” businesses, and wrapping your hobby in an entity probably won’t fool the IRS.
The good news is that if I understand the IRS publications correctly, we can deduct any spend on new gear from the income from selling old gear. So if you sold a $120k CS 80, don’t have receipts for the $250k you paid for it in the '80s, but plan on buying a quartet of Colossusses then I don’t think you will owe any federal tax if it all happens within the same calendar year.
If you are a professional musician/studio, then you can deduct like any other business, but you have probably already been doing that.