As the title suggests, I'm a newbie. I also thought it would be nice to grow a tree from seed so that I could go into the hobby with something I'd grown myself.

Didn't know that's a very hard thing to do. Despite that, I have a Royal Poinciana (Delonix Regia), that's around 6 inches and seems to be doing well (picture attached). It's from a starter kit so it came with dehydrated soil disks which I'm sure isn't the optimal thing for it to be in, which brings me here.

It's approaching two months old and I want to make sure it keeps up healthy/optimal growth. So: should I re-plant it in something more conducive? Is that akadama or some other soil to promote growth? Any other tips to making sure this thing lives and thrives would be greatly appreciated.

Also I live in US zone 6.

There are many years lett before you need to put it in a bonsai pot. Akadama is for growing trees in limited amounts of soil. What you need to do is to increase pot size or bury in the ground. Regular potting or garden soil is enough.

I would keep it in this pot till it is one year old, and then up pot it.
Or as Tropfrog has said, plant it in the ground for three or four years.