I promise you that like 90% of the creepy stories you've heard are people either exaggerating or just straight-up lying to sound cool on the internet. The kind of stuff that actually needs to operate over the TOR network doesn't exactly want to be easily discoverable by normal people.
You're no more likely to accidentally stumble across illegal / dangerous content while using TOR than you are while using any other browser.
In theory yes, but practically speaking trying to access a lot of the modern web over TOR would be at best painfully slow and at worst almost impossible thanks to DDoS protection providers like cloudflare.