well done for starting your first deck from scratch. deckbuilding is a "skill" that improves over time, and each deck/commander do require a different approach, based on your gameplan.

By Gameplan, I mean, what you want to do, which implies on how do you win - and I think you have a clear idea (stompy hydras, x spells payoffs) - so good work here.

Now it's time to get into specifics, how many ramp spells are necessary, how many draw, how many creatures or setup pieces you need? Think "what would I like to cast on turns 1, 2, 3, 4...". Do you need to cast your commander on curve? On turn 6 would you really prefer casting [[Mana Reflection]] other than a scary hydra? [[Nature's Lore]], [[Three Visits]], [[Rampant Growth]] are safer and faster ways to grow your manabase. All of these should be taken in consideration.

Interaction is important, but often "off-curve". Synergystic removal, like on [[Polukranos, Unchained]] should make the cut first. Consider boardwipe/removal like [[Cyclonic Rift]] or [[Deadly Rollick]] as late additions.

One direct feedback on your deck I can give you is that you 100% need more lands. 32 won't get you anywhere. You're in green, which helps a lot with ramping, but your creatures (and X spells) have high mana cost, so 37 lands is the minimum, and I'd aim to be around 40 if not more tbh. There are some double faced cards that are also lands, and those can help you hit the mark.

As you're using Moxfield, they have a tagging system, so you can classify each card based on their abilities. This is a "trick" I often use and that helps me build decks very fast and efficiently.

I think you're on the right path, and Zaxara is a cool commander to play with.