Should I evolve Pokemon before event ends

I just did a mass evolve but only because I wanted to create more space, but there's no bonus XP for evolving (like for hatching eggs) as during a double XP event (then it's quad XP if activate a lucky egg!). You should have 65-75 mons ready to evolve with a lucky egg so sounds like you should consider waiting and collecting a bit more.

Wait for more, the event doesn't give extra xp for evolving but some events do. I usually wait to have around 80 evolutions ready before poping a lucky egg for mass evolve.

This even only give 5x EXP for hatching eggs and 3x EXP for catching bonuses.

No bonuses for evolving.

That doesn't sound like you have enough to make it worth it, but a couple times during the event I used a lucky egg with an incense, and got about 80 percent exp of a normal mass evolve with a lucky egg. Although I still had about 40-45 evolves ready instead of 60 plus