Yep, you're pretty much spot on there. The resonator can be easily removed with no concerns and just increases the volume a bit.
Only tip I'd have is that it might be worth having spare gaskets to replace the old ones. The one between the cat-pipe and the centre section is a donut gasket as the joint is meant to be able to flex. If your exhaust is original then expect the donut might disintegrate when you change the centre section over.
They're not cheap though:
http://www.ebay.co.uk/itm/GENUINE-SU...item51b9e37258
You might be fine without replacing it (usual exhaust paste might do the trick) but it might blow a little. You won't know what condition of the original gasket until you take it apart unfortunately....