Naturalisation certificate will be handed over at the citizenship ceremony held in the local council.
You will need to call the council to find a place for you in the ceremony after you get the Naturalisation approval letter.
As soon as your Ceremony is held you will need to surrender your BRP (within 5 days). I don't think they have build the system yet to catch you at the borders if you are going to use the BRP but the disclaimer is that if you use , penalty is 1000£... so I will leave it to you to take the risk
My timelines read like this
6th April - Citizenship Ceremony
7th April - Cut BRP into 2, send it to the HMRC office through free post.
8th April - Apply for British Passport
28th April - British Passport Received.