Welcome to the club!
The centre pipe and the cat-pipe are two separate pieces. Fitting a non-resonated centre section will increase the volume significantly, removing the cat-pipe will not make it louder, but will make the burble more distinctive. As long as you re-install the O2 sensor no light should come on and a remap tweak won't be necessary for it, but from the sounds of it... you may need a map tweak anyway!
Edit: As for top end power, yeh the TD04 turbos do run out of puff at the top end as they are relatively small turbos