While a cracked screen likely wouldn't damage anything else on its own, it could lead to problems if any moisture or other things got to it and then cause problems with the rest of the device. Since the display would no longer be sealed.
"Matching Models" means aftermarket parts. Depending on where they are from and how they are made, they can be great or a problem. Choosing where to buy from is totally up to you. However, buy parts that are the 'same'. Not different features or 'should work with'. You need to make sure it is the right part.