It's very rare I use the sustain button itself other than for some of the organ sounds, but with any arranger keyboard I have always used a sustain pedal instead. If you plug a pedal in you'll have no problems at all and no need to set up custom registrations just for the sake of sustaining voices.
The SA voices are very easy to use, just adjust the key feel settings to how you play then you can trigger any effects you want by applying a bit more pressure.
Everything can be customised to your own individual tastes so don't worry about it