nikaah functions

Wedding functions

Q:

1. Which invitation is best in Islam for wedding- oral or written?

2. Is there a hadith that nikaah should be done after asr prayer?

3. Is it allowed in Islam to have separate function called Henna (mehndi) on previous day of nikaah for girls?

4. Can a wealthy man spend more on walima which will be done subsequent to the day of nikaah?

5. Is it permissible in Islam for a man and woman to suck or lick private parts of each other after nikaah?