Storing keystore on Google, aab or apk, privacy policy, content rating and more

Hi everyone!

It’s been a while since I published a game / app to app stores so I’m a bit rusty and have multiple questions regarding Google Play.

1- So there is an option to store keystore files on Google server and I’d like to use that.
a) How is the build and upload process work for this? Do we still generate a local keystore and upload the build with it?
b) Do I have to upload .aab or .apk file for this?

2- About .aab and .apk files,
a) Should I switch to .aab files?
b) Do we just upload it like we did with the .apk files before?

3- At the moment, I’m not collecting any data from my players.
a) Do I still need to provide a privacy policy or a simple page saying “we don’t collect any data” would suffice?
b) Is there a reliable template that I can use out there?

4- We’re thinking about introducing IAP in future updates but we don’t have anything at the moment.
a) Should we still be listing IAP for the content rating questionnaire or can we edit this later?

I guess that would be all for now. Thank you for your help in advance.