you probably have already learned this, but find EVERY nail.

get a powerful small magnet on a string, and drag it along the board surface to find nails.

also these help a lot too:

https://www.amazon.com/HOMPO-Metal-Detector-Pinpointer-Professional/dp/B07SDQ4Z3N/ref=sr_1_2_sspa?crid=1G30K7QS799CY&keywords=handheld+metal+detector+wand&qid=1662042992&sprefix=hand+held+metal+%2Caps%2C96&sr=8-2-spons&psc=1&smid=A2SMS1SALPK12F&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUE5UlNNWFczS0YzVDUmZW5jcnlwdGVkSWQ9QTAzMjMyMzAxWTYzRVNIRU1PODFSJmVuY3J5cHRlZEFkSWQ9QTA0MTYwMjUyWkFaU1ZLTlYxRUc5JndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==

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planer blades are very expensive. I had some hard pine i was planing, and had to buy carbide planer blades for my dewalt planing machine

also you probably noticed that a big planer will NOT take out a bow/cup in a floor board. that is because the intake rollers temporarily "flatten out the board", so the cutters do not improve it. I use a small hand-held planer to take down the high middle of a board, then flip it over and take down the high two edges. THEN i pass it thru my big planer machine.

after they are planed, you might have to grade the boards by finished thickness. use the thinnner ones on one side of the room, and gradually build up to the thicker boards