Yep, with baffle out you won’t be able to ride it long distances, and with baffle in it’ll kill the power. I got a baffle off a Harley dealer on ebay that fitted and made it ‘acceptable’ loud but didn’t affect the performance. Still no chance of passing a track day noise test though.
Yeah, most slip ons like the Akrapovic attach after the cat & just replace the fugly std end can.
On the gen 3 10R a lot of the actual silencing is done by that big cat/resonator box beneath the engine, consequently even a straight through race can won’t be unduly loud & shouldn’t need a powercommander. One will help though, not least because unlike the std fueling you can tune it purely for optimal power output through the rev range rather than be constrained by the noise & emissions regs that the manufacturers are obliged to meet in order to be allowed to sell the things in the first place.
If you’ve not done so already, then you may wish to consider getting yourself over to http://www.zx10r.co.uk/ & saying hello, lots of good 10R specific knowledge on there amongst other things.