OG Omnath is my oldest deck still running, so I will offer my opinions on your specific questions at least.
First, ramp style. In my experience lands > creatures for Omnath. Most metas aren't filled with mass LD, but board wipes are everywhere. You can also tutor for them in bulk and its fairly easy to get more than one mana out of them.
Memorial vs Chieftan is harder. I run both, but if I had to pick just one I'd run the Chieftan. Much easier to tutor and recur a creature.
Asceticism vs Archetype is another hard one. Again I run both. And despite my above statement about Chieftan, here I'd pick Asceticism. This type because, in my experience, enchantments are the least destroyed permanenet type. People usually pack very little targeted removal and sweepers that catch enchantments are even less common. As always, YMMV.
Queen/Spider/Hydra - Once again I run them all (what I notably don't run out of your deck are the *terrifying* creatures like Blightsteel, Vorinclex, and Eldrazi. I'm hardly saying you are wrong, I've just specifically tuned mine down for my LGS. Just wanted to explain where all my card slots are coming from). Queen and Spider are the best air defences green can get. I'd likely take Spider over Queen, since a repeatable sweeper (that you are almost immune to without Memorial out) is a rare find.
The Hydra is great, imo. I might actually run every card I can that lets me search for any land, since the best lands are even better in this deck. The fact that he gets huge is just gravy.
Heroic Intervention is a must have. I also like Wrap in Vigor. Its not as good, but there are only so many outs green has.
Then the tutors. I prefer to draw a lot in this style of deck rather than run a bunch of tutors. Partly as a preference to variety, and partly because I run the extra land drop cards and want to have more lands to play. You've got the good burst draw spells, but I also like a little steady draw. I run Mind's Eye (amazing with Omnath) and Lifecrafter's Beastiary. Good eye for getting Mirri's Guile, that card is so underused.
Last comment is about your lands. You definitely don't want too many colorless lands, so they have to be great. With only one landfall dude, I think the fetches are unnecessary. The LD lands you have are too meta dependant for me to judge. I do recommend looking into Deserted Temple and Rogue's Passage.
One last thing. If you find yourself generally going more tall than wide, Pathbreaker Ibex could be much stronger than Craterhoof.
Mind's eye kinda goes in and out of the deck. I just really hate the number of triggers it ends up generating. I tend to not like Rhystic Study and mystic remora for similar reasons.
Finale of Devastation joined the ranks of TnN and Genesis wave of the big finishers. I also recently picked up a Defense of the Heart. Defense of the heart obviously being pretty mediocre if you don't run the eldrazi monsters
Fore of Vigor is probably going to get a spot as well.
As far as Ramp vs Mana Dorks, my current set up is mana dorks because they are just so explosive, especially if I am ever doing pick up games 1v1. They also enable Natural Order, but I know there are also some ramp dorks too. I think your right though, that ramp is much more durable, but its also much much slower. I'd be curious what ramp package people do run in a more tuned list though.
I guess I like the idea of Heroic intervention and wrap in vigor, but I already play so much omnath protection I am trying to figure out what to cut.
I think the wasteland and strip mine are probably relics from when I first started playing commander and I had things like Crucible in the deck and more people seemed to play with maze of ith. They could probably be cut for forests at this point really. I think I went a little too hard on the colorless lands.
As far as fetchalnds go though, even though I only have Avenger as a landfall guy, with all the library manipulation, I was probably going to add in the Prismatic vista TBH.
I feel like I might have misread pathbreaker Ibix at some point because that seems really good as well.