I hire voice actors and pay for text to speech softwares, Speechelo, talkia or any other software is good enough as long as they speak natural.
you can't check the video before uploading, Upload, make it unlisted see if there is no checks and go live. if you are trying to manipulate the system, than sooner or later it will become copyright.
yes you have to verify google adsense account to get paid.
I would wait at least 180 days before making any action of that account with 50 videos. ( also, keep uploading as this will give you more impressions on all of your videos)
Honestly review your channel and check for stats, like retention and CTR - if they are low change the quality of the content. if they are high, aim for keywords IN THAT niche that can be combined with other niches. People love to see something new, not just things they already heard in the last 5 years. Which may also cause your channel to be invisible.
take a look at the best performing videos of yours and analyze the drop of viewers.
ONCE YOU FIND "AHA", create content only about one theme, that your audience are finding You.

also, don't forget to check for competition and search volumes. They are important, unless your theme is nothing to do with that.