Please refer to the post above; "If you wish to refer to the Japanese version of GT5rologue, then use the term Japan, Japanese, JP or JPN. Use of "Japanese" will not be tolerated as it is a racist insult."
Concerning the number of players in an Online event it depends of the event but yes the maximum is 16 for some of them in the Japenese version.
The JPN version is 100% identical to the Europian version once you have downloaded all the updates, so in answer to your question, yes! But only on some races (more advanced ones, not beginner ones).