began or was begun?

I prefer "began."

Creativeguruby welcoming the chief guest.

I prefer "We began the installation ceremony by welcoming..."

The ceremony didn't "begin itself."

For me, there is no problem saying that the ceremony "began", but the next part doesn't fit: it would mean that the ceremony welcomed the the guest, which doesn't make sense. With "was begun", while arguably the dangliness of "welcoming" is reduced, the sentence is horrible to my eye. I would recast it, e.g. as Barbara has suggested.

I agree. Perhaps that was my problem with the sentence and I didn't recognize it as such. The ceremony can't welcome anyone.