Attending celebration of life event - etiquette questions (my father-in-law passed)

My father-in-law passed away recently and the family is holding a celebration of life event next weekend instead of a traditional funeral. I've been to mostly traditional funerals before, so I'm a bit uncertain about the etiquette differences and want to be respectful to my spouse and their family.

A few questions:

Attire - The invitation says "celebrate his life" but doesn't specify dress code. For funerals I'd wear all black, but is that expected here too? Is business casual okay, or would that seem too informal?

What to say to my mother-in-law - I know "I'm sorry for your loss" is standard at funerals, but does that feel too somber for a celebration of life? Should I lead with a happy memory instead? I'm worried about getting it wrong when I first see her.

Gifts or contributions - Do people typically bring anything? Flowers feel very funeral-like. The obituary mentioned donations to a specific charity in lieu of flowers. Should I make a donation beforehand, or is a sympathy card still appropriate?

How long to stay - Is there an expected timeframe like with funeral receptions? I want to support my spouse and be there for the family, but I also don't want to overstay if these tend to be shorter, more informal gatherings.

General vibe - This might sound odd, but how much "celebration" is expected? Is it okay to laugh and share funny stories, or should I still keep things more subdued and respectful? I want to match the energy the family is setting without accidentally being too upbeat.

I really want to be supportive during this time and honor my father-in-law's memory appropriately. Any guidance from folks who've attended these would be really appreciated.