Hi Tia, I´ll try to answer some of your questions..
-before the wedding - wedding-eve party
To clarify, the plates which will be crushed by the guests, are not your plates. The guests will bring old dishes, lavatories and even toilet bowls (in case you have really nasty guests) with them to crush. Bride and groom have to sweep up the broken dishes. But be careful, no glass should be crushed because this will bring ill luck. So regarding to the dent in the budget, you will „only“ have to pay for food and drinks like every other party. The only thing, people don´t want to have such a wedding-eve party is, to pay 2 times for the guests – 1 x at this evening, and at the wedding day, too.
-wedding candle during the wedding ceremony
this wedding candle can be made from you or your family or could be bought also. It will be lighted up within the ceremony at the church e.g. The meaning of the candle is to give light to the common live´s journey from the couple.
-cutting of a bed sheet don´t have a specific name in German. We call it „Hochzeitsherz ausschneiden“
-saw up of a tree tunk
You will find a prepared tree tunk and have to saw up the tunk together. Bride at the one side of the saw, groom at the other. This is very exhausting, especially when the weather is hot. It´s called „Baumstammsägen“ and the meaning is that the couple will be strong enough together to force the future.
-the wedding couple has to drink together from a wedding cup
no, not at the same time. First you are drinking, than your groom. This is a kind of game which can be done within the whole party.
-cutting of wedding cake:
definitaly you have to cut it together! But the one who´s hand will be up, the one will be the „boss“ in the family. For example: While cutting the cake your hand is up and your grooms hand is below your hand, so you will purchase in your relationship.
Hope this helps