star - What do we know about the characteristics of stellar objects, 13,3 billion light years away from us?

Holger,

I highly recommend you check out the NASA story on the discovery MACS0647-JD, which includes many dimensional facts (mass, distance, age, etc.) and comparisons:

http://hubblesite.org/newscenter/archive/releases/2012/36/full/

From the article:

The estimated total mass of the stars in this baby galaxy is roughly
equal to 100 million or a billion suns, or about 0.1 percent to 1
percent the mass of our Milky Way's stars.

---

Measuring the mass of a galaxy is very tricky indeed (especially one as far as 13.3 billion light-years from earth!), but there are a couple different methods that can one can use, see here:

PSU Astro Measuring Mass of Clusters

And this Physics Stackexchange thread as well:

http://physics.stackexchange.com/questions/123/how-does-one-measure-the-mass-of-a-galaxy-and-other-such-large-quantities