Ah, most of this knowledge is coming from people asking questions to Alf on IRC, and is not the kind of info that Shinji himself would really know for the most part. But I will try to sum things up for you. This is going off of my head and should be taken with a grain of salt as not everything is 100% certain or likely correct. That and Shinji does not know about a lot of this.
Ayaka - Japan Champion. We know her at this point.
Olu - African Champion. Not much more is known about him other than he seems to be able to manipulate earth and can make a quick sand attack. An aggressive leader that holds himself as the rising star now that Africa is the rising power due to the power vacuum caused by Dumbledore's death. In a lot of ways he is Shinji as a transfiguration master. With a tank like form, earth powers, but replace ofuda with wandless african magic.
Mishca - Russian Champion. Headstrong person that looks down at people who are not as militant as him, such as the more cerebral schools like France or Hogwarts. Feels that Shinji as a champion is an insult due to his age. His family was the family that ultimately kicked out Zouken from Russia. Family has sworn to end Zouken's bloodline. Possibly has Templar connections.
Lestrange - French Champion. We know her at this point.
Sondrol - Nordic Champion. We mostly know her at this point, but she is rather good with stealth, and hit run attacks. Tends to favor the potions in their vapor forms, or injecting them straight into the body.
Elesa - American Champion. We know her from her chapter. Beyond her ties with Ayaka, she has closely worked with Ramona in the past and has also worked with Ku'. Has been feeling out the others, collecting intel. She can not be killed and will survive easily an AK hit due to her Chosen of Gaia status.
Ka'aukai - The Fleet champion of the Pacific. We have seen his personality somewhat last year. But tends to be calm, and calculating. The water user of the bunch with spiritual abilites. After meeting Shinji last year, he asked around Japan about him, learning what info they knew about him as he was curious about the Japanese boy that went to Hogwarts. The Fleet has partial ties with the Illuminati as they both been working together to guard the sleeping Elder One deep in the Pacific Ocean.
Libatius - Brazilian Champion. I do not know that much on him other than he is rather good with potions even by the normal champions standard. Has a specialty with poisons. He tends to like other people that are as knowledgeable about potions as him. Knows the martial art of capoeira. He is not super tier champion, but not horrible also.
Parambir - Indian champion. Knows a bit about fighting with India style swords. He is considered to be at the bottom of all the champions with Shinji. He is not super good, and tends to have a similar wand fighting style as Hogwarts due to his school being an off shoot of Hogwarts. Not actually happy that he is considered to be from a back water school when the Shinji, the 14 year old is not even from Britain himself is champion to the 'elite' school. He is in over his head from what I can tell.
Ramona - The First Nations of Canada champion. She is anti-spiritual powerhouse with her spiritual attuned skill set, but is also a healer and not a warrior by nature. She is the investigator/researcher half to balance of Elesa's full agent in their field work since they have worked together before.