Don’t think all your cards are mint, they most likely aren’t. Spend time looking at them and figuring out conditions and then look at ebay solds for either sets or individual cards that match your edition, set and condition. Don’t look at PSA 10 and value cards at that price.
Generally, when I try to value a card I search the specific card + condition on eBay and go to the sold listings. It should show you the most recent sold prices of what you were searching. Usually gives me an idea of what to price my cards at based on their condition.
Selling a collection will not get you anywhere near market value. You will be lucky to get 50% of your estimate. Time is money. You want to sell for a good price, put the time and effort into the research and selling it piece by piece. Most if not all buyer will not sit down and go over every single card. How much time would that take to give an accurate offer?