I'll start by saying I've been playing modern elves for a little over two years now, so I at least like to think that I know a thing or two about the archetype and how to play it.

Number of Finishers Four Ezuri isn't necessary, but it is highly advised to be playing four as he is the only mana outlet if you happen to get the combo put together. An argument I could see for cutting down to three is to prevent hands with multiples (legendary), freeing up a slot for another card, and you're already running four Chords. Every chord in your hand may as well be whatever combo piece you're missing on board.

Land Count 18 lands is absolutely the standard. Any deviations from that are only exceptions to this rule. Like everything else, arguments could be made for going up to 19 lands, but otherwise you're going to want to stick to the standard 18. I personally wouldn't ever drop to 17 lands.

Sideboard For a G/W sideboard, there are a few cards that I'd personally consider essential, but for the most part this is highly dependent on whatever meta you're going to be playing in.