NEW DECK (Question)

Good day Al,

We bought our dream home on the coast three years ago. We now have spent the last three years completely renovating and restoring our dream house. Now that we have all the necessary work completed, we want to add some amity, like a custom redwood deck.
We have the deck plans drawn and now we are preparing to get bids from contractors.
We have talked to some contractors on redwood decks, and some said to seal the deck with water repellent, and some said that redwood does not need to be sealed. The prices are very different, depending on to whom we talked.
Is there anything else of which we need to be aware as we get prices, and should we seal the redwood? If so, why?

Thanks Eian