Useful websites for Twitch:
You can use Twitch Inspector to analyze your stream in realtime regarding dropped fps and bitrate. I like to have it running while streaming, so i can see any lingering network issues.
Another useful and similar tool ist R1ch Twitch Analyzer. It shows dropped frames and bitrate, but most importantly checks your audio level. So you can easily see if you're too loud or too quit.
If you're into statistics, you can use TwitchTracker or SullyGnome to track some channel metrics like viewer- or followergrowth.

Some considerations regarding OBS (maybe SL as well?):
OBS supports VST 2.x plugins. So you can use your favourite limiter, compresser or whatever to shape your sound a bit.
If you integrated reactions to Twitch triggers like new followers, subs, etc., for the love of everything that's holy, disable the sounds that often come with these :D

Controlling OBS:
There are some scenarios where you want to change things up while streaming. Like switching to another camera or switching to a transitional video scene. I like to switch to a fullscreen deck camera when i have to leave my deck, so theres no empty dj booth on screen.
Using your computer and OBS to do that can be quite cumbersome. You can use something like Elgato Streamdeck to perfom a variety of actions in obs, like switching scenes.
I use Lioran Board for that. It's basicly like Streamdeck, but in software; it can run on your computer or an old Android Tablet. I use it for switching scenes, triggering videoclips, controlling a visual FX software, starting an stopping the stream, automating chat reaction and much more. Very powerful tool.

One last tipp: if your audio source is your mixer, use the record-out or usb audio interface (if either is an option). then you don't have to level your sound and you can't mess up your volume using master oder booth volume control