Some questions

Hi, I don't know what the tags mean so I chose one at random 😭 but yeah I'm getting rats and I'm super excited but I feel like I've read a whole books worth of blogs so far and still don't get some things 😂 don't get me wrong, it's fun to read about it but for that reason I wanted to ask y'all to clarify some things for me.

1. bedding - I found a well reviewed substrate (Chipsi - let me know if it's actually not good for them or something) that I would use, but like now (when my rats arrive) I fill the tub in my cage with ~10 cm and that's then it? Like that's then good for burrowing and for gathering their pee and for comfort? There's just so much about this topic online that I'm not sure if I need multiple things for multiple purposes. And I change it (with 4 rats) every week/when it gets smelly?
2. food - I read you give them their basic food and then some fruits and veggies once in a while and more protein for the babies, but how does that work with the fact you sprinkle their food into the bedding so they look for it? Do I still need to give them the exact amount of food and veggies and protein etc? Because I read they only eat as much as they need, so like if one is missing protein it can look for it and eat it - or is it supposed to be more controlled feeding? Will they show signs that they're missing something in their diet or do I go off of the percentages and amounts I read online and hope they're healthy?
3. babies - the ones I'm getting are gonna be 8 weeks old, do I need to adapt all of the guidelines I see online about cage enrichment, bedding, food etc. to that? Or is it the same deal, just a bit more protein in their diet and smaller distances and heights in cage since the babier are smaller?