What's your budget?
What is the win condition of this deck? How do you want most games to play out?
My general plan is to grind out games with card advantage from Damia, sphinx, and the discard for opponents, then slowly chip away at them with the midrange fatties like aeon chronicler, or steal their own things with guile.
That approach seems too scattered to be effective.
Discard tends to be very ineffective in EDH since there's plenty of buildup time and draw power available.
Midrange fatties are only mediocre in EDH. They get ruined by all of the sweepers and removal in the format, and you're just not doing enough damage for it to be truly effective.
I personally find BUG to be best at combo-control, but if you're aiming for a more casual approach, you should probably avoid that. Reanimator is a decent BUG strategy, but The Mimeoplasm is usually a better general for that kind of deck.
You should avoid running creatures just because they're fatties. For example, Stormtide Leviathan doesn't offer you any extra utility, making it a dead card a lot of the time. Something that can have multiple applications outside of combat is very viable and valuable in EDH.
Lands: looks good however, I don't see any legendary permanents that need Minamo other than that my only other suggestions are personal preferences which can get pricey
Creatures: Arashi feels out of place and there are better, broader removal options, you might like Terastodon for instance. Eternal Witness is vastly better than archaeomancer. I like Dark Impostor but I'm not so sure I'd play it personally since that activation cost is awfully steep. Maralen of the Mornsong is a nice pick but it doesn't have much synergy with Damia this doesn't mean you should drop her though, you might want to consider Necropotence not only will it get past Maralen's pesky draw lockout but it's fantastic even without Maralen. Vanishing might be a good choice too although I'd recommend against adding a card specifically for another, but it is something to consider. Stormtide could probably go, you don't have anything which is going to benefit from it and it pushes you into finding options to get around the lack of islandwalk. Void Stalker can probably go too but it is a really neat creature and it does help out some. Other creatures you might want to look at are Mystic Snake and Draining Whelk to help out guile as well as card:Tomorrow, Azami's Familiar and Arcanis the Omnipotent for the obvious card draw interaction.
Sorcery: you're running an awful lot, and some could go once you get a clearer idea on which direction you want to go with this. I'd drop all is dust but only because its one of the more higher costed board wipes that said Plague Wind costs as much but it won't touch you plus if you build right to where you ramp and accelerate your mana, which you should because you have access to green spells so take that with a grain of salt. Some other ones you should consider are Decree of Pain and Mutilate . I'd also recommend Skyshroud Claim to either replace farseek or run alongside it.
Instant: not much to say, although I'd recommend at least Spelljack
Enchantment: asceticism is nice, might not be right for this deck in the future but its nice. I'd say drop grave betrayal. Consider stuff like Phyrexian Arena , Mana Reflection , Thought Reflection , Defense of the Heart and perhaps even doubling season ( although at the moment that would only benefit planeswalkers) just to name a few.
Planeswalker: Tamiyo, new Jace ( although tMS and memory adept could work too), maybe even one of the other Garruks either replacing or along with it, tezzeret the seeker if you end up with enough artifacts to make it worthwhile (don't forget artifact lands if you run him) , Liliana Vess and/or Liliana of the Veil
Artifact: just drop Akroma's Memorial. If you end up with a good amount of permanents with activated abilities I'd say Rings of Brighthearth would become an auto-include. Mana fixers like Darksteel Ingot, Gilded Lotus, and Coalition Relic are a must as well.
if not, OP, then you need to change that out
This guy's just confusing. Anyway yeah I would play something like that or Worldly Tutor