[Avodah] questions regarding pidyon haben

[Ben Waxman]

A neighbor has asked a whole bunch of questions regarding pidyon haben. 
Please send any answers to the list as well as to: ziggy at netvision.net.il.

Thanks
Ben

I am very curious about several things. Please answer to my email.

1) how much should the coins used be worth?

2) Is it an accepted practice to put garlic and sugar on the tray and
if so in what form?

3) Is it an accepted practice to put jewelry on the tray?

4) (not relevant)

5) Are there any other minhagim (or halachot) that I am have not
mentioned?

Most importantly (for my own understanding and please forgive my ignorance)
- what is the big simcha? The child should have served Hashem in a very
special way but cannot because of the sins of the bchorim before him. The
Cohen has a reason to celebrate but what exactly is the family of the bchor
celebrating?