Are there any restrictions for injecting ads and subscriptions into the app?

Question

Android

I plan to release a free Android application. And then develop it.

1) Will it be possible much later to embed ads + subscription to some advanced features in an application already published for the future? Or do these things need to be included in the 1st version already now?
2) Is the above physical. face? That is, getting money from advertising and subscriptions.

Answer 1

1 - you can
2 - depends on the ad provider, but usually you can