99 Civic Ex. I have a DC 4-1 one piece header with no cat/exhaust system. Cat got clogged/broken and stock muffler fell off.

I purchased a Yonaka 60mm exhaust system, and a "high-flow" Yonaka 2.5" catalytic converter which has yet to arrive.

I did not realize the size of the cat till after it shipped, basically im looking for feedback/knowledgeable advice.

From my research, the header outlet size is about 2.0". The cat in/outlet is 2.5" and the cat-back exhaust is about 2.36". I figure since the cat is the most restrictive part of the system the larger size should benefit flow.

I have a few questions about this setup.
1. Will this setup run fine?
2. Should I purchase a 2.25" cat instead?
3. Should I purchase a header with larger outlet?
4. If i keep the current setup, what should I expect a shop to charge to fit the header/cat/piping (if they are even able to)

Thanks in advance for the reply's