The given link says
In case this information is widely available and you have been previously informed on the specific info, your “thank you for letting me know” could sound sarcastic and bitchy, so careful… especially if it is your boss reminding you or highlighting something… maybe best check on this infor [sic] in depth before thanking for it!
Notice that in the scenario, the information is "widely available". If the information is somehow obvious and it's likely that you already knew it, then it could sound sarcastic. In writing, I think it would be harder to tell how you mean it, but in speech, it would be clear if you use a sarcastic tone.
Actually, I think any of the phrases could sound sarcastic or "bitchy" in a scenario as described above. However, if you have good intentions and use a polite tone, then it should be fine and you shouldn't worry.
That said, I think they're all good, except number 3. You need an "of": thanks for reminding me of that.
I know remind can be used when I already knew something before then someone would remind me in case I forget, but can it be used when I know it for the first time?
Technically, no, because they wouldn't be reminding you. But if you want to give the impression that you knew it, then you would use it. Again, be careful, as it might sound rude or condescending.
And good to know seems okay when someone tells me something about themselves, can I use it when say someone leaves a useful comment under my post?
Yes, you can use "good to know" when someone tells you something useful.
If you want to sound a little more formal, you could use something like
- I (really) appreciate your comment/response. Thank you.
- Your comment/response was (very) informative. Thank you.
More casually, you could say
- Thanks for the info/information!
- I didn't know that. Thanks!
- That was useful. Thanks!
Similar to remind as above would be
- Oh yeah, thanks!
Sometimes you say "oh yeah" when you remember something that you should have known, or when something should have been obvious but you didn't see it at the time.