Why are some of my apps running non-stop?

Is it the way you set it, im on a free tier, or I guess im trying stay so, will my apps ever go offline or is it just how my apps would still be? 24/7/30 online and nothing will charge me???
On a NOTE: since i’m trying Fly for first time i had mistake and created 2 wrong Apps, so I removed 1 of the wrong but kept the other which eventually went Offline.

Question 2: had I not removed the very first wrong app, and if i had 4 apps now i would have been charged, if yes, how much? I read documentations and there is lots of comparison to Heroku, but there I was limited to 5 and I must pay to unlock more apps. Would you have thrown me an error “you will have to pay in order to have 4th app” if I didn’t removed it myself??

Question 3: I cant quite have Nodejs+Postgres on a same Dyno/App without a lot of workaround and using Docker, is that right? I honestly expected Postgres to be attached to my Node the way Heroku did, but if 1 server takes 2 Apps … that leads me to question 4: do I have to pay per Dyno/App (im confused with the terms) or do I pay just for “data/storage” plan and unlimited Apps/Dynos are on me limited to my chosen storage plan?