A limiter is great for keeping a signal from getting too loud when someone gets too up on the mic or excited, the plugin your looking for to make quiet voice louder is called a Compressor. It takes a audio signal an boosts its gain to match the louder parts, I can reccomend a free compressor built into Reaplugs which also comes with all the plugins from reaper which is a amazing digital audio workstations. I personally run a little more advanced setup with some paid plugins I've had for years from back when I did audio engineering. I like to start my audio stack with a noise gate, then add the equalizer, then a limiter and then my compressor as it boosts the quiet parts to match the louder ones but the audio can't go past a certain db because the limiter. One recommendation I can make for people starting out with audio engineering is to get a little program called VST host, then import your plugins into there an set your playback and recording device an build a audio stack in there an adjust settings while listening to the output an it'll give you a better idea of how you should setup your plugins inside OBS. This is just my 2 cents worth an I'll gladly expand upon this info if it's helpful.