It’s always advised to use what you already have. That way everything will be profit. To give you some numbers. Last month I had ~7TB stored and made ~$25 across my nodes of which ~$7 went into escrow. During testing and surge payout it was much higher, but these are the number you should expect, everything more is a bonus.
So if you buy a new hard disk, you can roughly estimate how long it will take to pay for it. Keep in mind it will take some time to fill it and at the beginning most of it goes into escrow.
3.5" SATA any time if you have the choice. Read the forum, most problems people have stem from USB connected drives. And avoid SMR drives.