Looking for a tool to create explainer videos with some 3d characters

I'd suggest taking a look at Adobe Character Animator - that software makes it pretty easy to create talking characters -it comes with a timeline too.

Rick is right that you'd probably need additional tools, but I've found CA a pretty simple tool to get started.

After Effects is a motion graphics and visual effects application designed and only well suited to creating shots that you cannot create in a video editing app like Premiere Pro. The 3D capabilities of After Effects are limited to manipulating flat X Y planes in 3D space unless you invest in 3rd party solutions like Element 3D or others. You canto extrude Text layers and Shape layers, and you can bend other layers if you use the C4D rendering engine, but many features like blend modes and even motion blur are disabled with that rendering engine.  

After Effects does not include tools that let you create or animate 3D characters. AE can integrate (composite) animated 3D characters and scenes into a final shot. Those shots need to be edited into a movie using Premiere  Pro or another NLE.

I have created many explainer videos using After Effects as the tool for animating graphics and 2D characters. The comps are rendered using a visually lossless production format. The compositions are never longer than a phrase or sentence. The final editing, sound mix, and even final color grading are always done in an NLE.

Adobe Animate is an excellent tool for creating shots and sequences using 2D characters (cartoons). Blender will integrate reasonably well with After Effects, but a professional would never try to create an entire movie or explainer video in a single Blender scene. It's the same with After Effects. You create your shots, render them, then edit them. 

You are going to need a lot bigger toolbox than just After Effects. I hope this helps.