The testing phases can be bought separately from pledge packages right Now even :P
Unfortunately not everything will be available for purchase separate. The base 45 dollar Elyrian package is essentially a base version of the game, and whatever you see in the a la carte store can easily be added to it if you want to buy a little at a time.
What I would personally suggest though is to just slowly increase your pledge package until you are at the level you want to be at, since you only have to pay the difference in price from your current one when upgrading.
That being said, if you dont want to start the game during exposition and customize a family, going even as far as bloodline might not be necessary as thats the main selling feature of the top 3 tiers.
Ah, do note that all testing phases and pledge packages will leave the store eventually in the future ad we get enough people for a testing cohort, or simply get closer to specific stages of development. So if you decide to wait id make sure to at least keep an eye out for those announcements so you dont miss out.