Demoting from one tier to another tier?

I just promoted to Plat 4 after months of grinding for it and I'm really proud of myself for doing so!

However now I'm a bit scared. I know there is a 5 game demotion shield and out of those 5 games I won 3 I believe, lost the other two. I just got out of another losing game (we got shitstomped) and I am now sitting at a healthy dose of Plat 4, 1LP.

I was told by my friends to stop playing ranked if I want to keep the rank I'm at right now, but I think I can climb a little higher this season plus I'm addicted so I kinda gotta play it and can't wait until early next year to start again :p

Anyways I was just wondering if demoting from one tier to another tier is the same as demoting from one division to another division? I demoted from Gold 1 to Gold 2 about 3 times before this, and each time it was about one or two at most games lost at Gold 1, 0LP and then I'd get demoted.

If I am Plat 4, 0LP how many games would it take to demote to a previous tier? I was told you may get a warning telling you that you're dangerously close to demoting. I was also told I need to be at an entire tier lower MMR in order to demote (which means my MMR has to be Gold 4? Is that right?) from Plat to Gold but I haven't really gotten a definitive answer. Even Riot hasn't been too clear to me.

That's why I'm asking here, since you guys have personal experience!