How much amusement is allowed? Is there any protocol for weddings? Please answer according to Sunnah.
The best model for marriage and wedding according to Sunnah is the marriage the Prophet made for his daughter Fatima Zahra S.A. All parts of this marriage and wedding were managed by the Prophet and because the groom (i.e. Imam Ali S.A. and cousin of the Prophet) was an orphan from childhood, and was raised and trained by the Prophet and, in fact the Prophet was his like father figure, so in this marriage the Prophet was the manager of the marriage for the both sides and, thus this marriage can be considered a perfect marriage in Sunnah because all of it was managed by the Prophet and can be considered a 100% Islamic marriage based on Sunnah.
How much amusement is allowed?
A free dinner was given to the people who attended and, some had happiness when the bride was going to her home.
Is there any protocol for weddings?
Yes, out of the obligatory rules in Fiqh there are some recommendations. For example, the Mahr (wedding gift) is better to be small and not excessive. The male and female guests should not be mixed. the bride should not show her 'adornments' to men (unless of course, they are her husband).
On top of these, there are more referred to in the following books.