dream porsche

I am purchasing a used catalytic converter which I will have gutted and
installed in my 1996 993 c4s.
I have read remarks from all the knowledgable folks out there and I
have concluded it will be ok, give me a meatier sound and maybe make my
car more drivable.

I will also have my airbox drilled.
Any final comments from those more knowledgable than I?

Also....When I first got my car I checked my oil as recommended
and my dipstick was dry. I added oil, and the next morning after my
60 mi. drive to work I found oil spit all over the rear end, wing and throughout the engine compartment. My mechanic explained what I did wrong but now when my car idles, light smoke comes out over both tires.
The car runs great, temp. cool ect. My mechanic cleaned engine area as much as he could. Any thoughts?

my oil level gauge stays flat in the red most of the time....even when in idle mode. So I am afraid to add oil even though my dipstick shows its a little low.
Any advice to a non mechanic person?????