1 Can somebody explain the main differences between apklib vs aar files ?
Couple differences that come to my mind, in addition to the ones you mentioned
aar
doesn't contain source codeaar
can contain custom proguard file and custom lint rules
2 Can Maven use aar ? Can Gradle use apklib ?
The Android Maven Plugin supports aar
since version 3.7.0.
Gradle doesn't support using apklib
dependencies but you could export your android-library
as apklib
(see this post).