We have been to the Takayama Spring festival, it was verry nice. Street parades all over the place. We visited during day time,all day long there are things to do, I do not know how it was in the evening. I would suggest you make it a day trip this is much more relaxed than half a day.

You get to Takayama by train and walk into the city very easily.

If you are thinking of a daytrip to Takayama, it depends where you are using as a base. If you want to stay near Takayama, consider staying in Furukawa which is only 15 min. by train from Takayama. It would be a good idea to stay in Furukawa if you go for the evening parade.

That is a misunderstanding. The festival is ranked as one of Japan's three most famous festivals that feature festival floats. Not the third largest.

1) How do I get there?

How to get to Takayama:
http://www.japan-guide.com/e/e5908.html

Where in Takayama the festival takes place:
http://www.japan-guide.com/e/e5909.html

2) What time should i go?

The best visit in my opinion is from around noon of the first day until around 10pm to see the evening parade.

What else is there to do in Takayama?

Here you go:
http://www.japan-guide.com/e/e5900.html

Is this a day trip? or just half a day?