You probably don't need a mixer anymore advanced than the soundcard already in your computer... though you might need software to really exploit it... you should be able to do this with windows volume mixer:
Set gain to +10dB, set recording level to like 90-95% (test where it starts to distort by enabling mic in the Sound Output controls to hear)
And finally, there's no way to avoid getting a decent mic but there's no need to spend hundreds on it.
And finally I reckon you should charge access to your vods... do like seasons of 10-20 sessions and sell access to the vod for $5 or so.
Will help monetize the effort you're putting into all the streaming and help you cover the equip, power, hosting costs etc but also, increase your return on training session time with a kind of residual income you'll be able to enjoy even while attending tourneys.
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