Is there a way to figure out which users are active users and is there a way to add and send the same messages to several users at once?

I have no idea. Try Skype's user support forums. That's what they're there for, I'd wager.

In Korea there is a voice chatting program called TalkOn.

Foreigners can get an Nate ID and then log on to it and go to the 외국어 room (foreign languages room) where there is usually Japanese, Chinese, and English rooms.

Is there a similar program in Japan?

Go to Koebu.com

It's random Japanese voice chatting site.