Gain / Trim plug ins

Sonar's input (gain) knob on each channel does adjust the gain into the channel so yes, no need for an additional plugin there. Most plugins have input and output gain controls as well. It's important to remember to check the gain between plugins. Most plugins have a sweet spot when it comes to input gain. Most analog plugins can be driven too to get different character out of them. Take a look at the plugin's manual for it's recommended gain range as they vary from plugin to plugin, but you should be able to do it by ear to hear the best results.