At this moment the post install world file is loaded with unwanted deps that result in problems when you want to emerge world.
You can use emaint --fix world
and manually clean out the world file to a normal size. Where it would have sane stuff thats in your world.
This will be worked out before the next release anyway.
But yes, with this out of the way ofcourse you can first use entropy and once satisfied start using portage from that point.
But be aware that from then there is no way top get back to entropy unless you let entropy reinstall nearly everything.
In addition, we are working on a CoreCD with text-installer that will be the absolute minimum to start working with entropy and/or portage. Kernel+toolchain from entropy...you get the idea.