Not currently in a test phase, we are in like a pre-pre-alpha phase. The first test phase we will be in where we can Participate will be Prelyria, but we do not have a timeline just yet.
We just finished Map Voting where each server was able to select their starting continent they will be playing on.
We are about to hit Domain and Settlement Selection here soon though, one of the prelaunch experiences where title holders (mayor and up) will get a chance to stake out and claim their land on an overview map.
And to answer your other question, yes. If you buy the Elyrian package today, you can upgrade it by paying the difference later. But! some of the packages are only around for a limited time, as you can see here so don't wait too long.