Tateyama Alphine advance ticket require?

I am planning to visit the Tateyama alphine route on 30May2016 which is a weekday. Should I purchase the ticket from Dentetsu Toyama station or the Tateyama station. If I purchase ticket on the day, will I able to get on the cable car early enough allowing me to do a return trip to the Dam ? Looks like it will take 7 hours return just on travelling. Any help most appreciate. KL

Should I purchase the ticket from Dentetsu Toyama station or the Tateyama station.

I am not familiar with your itinerary. But assuming that you start you start tarveling from Toyama, then you can and should buy the entire ticket at Toyama rather than buying separate tickets for the Toyama-Tateyama section and the rest.

If I purchase ticket on the day, will I able to get on the cable car early enough allowing me to do a return trip to the Dam ?

It depends on how busy it is and how early you start. On really busy days and with a late start it may not be possible.

As for the question in your title: No, it is not required to buy tickets in advance. But it is possible to make a reservation for the Tateyama Cablecar (unless you use the Alpine-Takayama-Matsumoto Area Tourist Pass):
http://www.alpen-route.com/ticket/en/

When I make a reservation, do my credit card get charge immediately ?