How to import models from BlockBench?

At the moment there is no such possibility and it is not planned. The thing is that in BDEngine you create models only from what you have in Minecraft, i.e. from blocks and items. In BlockBench you create completely custom models and therefore BDEngine is not able to reproduce such models.

Is it possible to make transparent pixels in Player Head?

Yes, but partially. You can make transparent pixels only on the second Player Head layer. The first layer does not support transparency. That's how Minecraft works.