A new president comes in and shatters the record for Executive Orders. But every single EO he does is essentially “repealing” 200 years of grossly unconstitutional acts of congress. Each EO abolishes, repeals, cancels, or suspends, some government program or agency like Social Security and the NSA.
If by “unconstitutional acts of Congress” you mean “statutes,” a president cannot do this. A president can veto a bill, but if Congress passes it over his veto, he can go to court about it or refuse to defend it when some state or citizen goes to court about it; rarely — only in extreme cases — is he justified in ignoring it on the ground that it’s unconstitutional.
A new president comes in and wishes to “cancel” all previous executive orders which are still in effect… What does he have to do to do this? Issue a new EO saying “all previous EO’s, except for this one, are done now?” Or is there some other process for “canceling” previous executive orders?
If a president wants to repeal existing regulations, he generally has to follow the Administrative Procedures Act, which requires him to post the regulatory change he wants to make, take public commentary for a set period of time, and then promulgate the new reg(s).