Those are all *choices*. I inspected a few people on the leaderboard and I saw some re-rolling their chests to elite%, some to armor. No one with life% so far, so I guess it's one or the other. I saw about 50% rolling for ranged, 50% for melee. It doesn't really matter.
Armor is probably best, because the rifts of your choice are non-elite summoner rifts. If they have more melee or ranged damage... no idea. If you can re-roll it test one or the other. It's not gonna be the make or break thing in the end.
2) Keep in mind that we don't know if that elite damage works (Furnace does not, see here). It probably does, but then you already have Stricken elite damage so it probably adds more like "only" 6% elite damage. Sacrifice up to 1k vit for that (which gets amplified by all the life%)... not sure.
3) Give me that amulet. Now.
4) On GR100 your killspeed will be higher, thus your Archon stacks will be higher, and thus your IAS will be higher. That's why I think IAS is superior when you're pushing. When you are well ahead of the timer after a gg first map and then you get the second map and "just need to clear 20%" in a mediocre, no-summoners map... you might regret your choice of skipping IAS. But who knows. A lot of if's and but's. As always with the RNG-heavy pushing. It depends on how much fishing you're willing to take and how many rifts you want to throw just because they don't fit your gear choice. Keep in mind that beast/human rifts are particularly juicy because of Pig Sticker, so here's one more variable to take into account.
6) Elite damage reduction doesn't show up in the tooltip comparison, afaik. I inspected a few people and saw the majority going for elite damage reduction, but that was a while ago. Not sure about Balam. Always take into account a top player's ability to troll everyone though Also, was he maybe playing with Ice Armor? +60% armor from Crystallize makes a difference of course. But I guess you never want to give up Force Armor.
2) Only one APoC, so in that case belt. People who use Swami with APoC usually roll off APoC on offhand for the missing vit roll from helmet.
3) Not sure. Not many people have those, inspect some top wizards. I personally would go for IAS though, as it directly impacts damage and if you play well, your Archon downtime is short enough even with 1-2 CDR rolls missing. But I've heard a lot of people say CDR > IAS > int. There's not a lot of people pushing 105 (I'm certainly not lol), so you're pretty much on your own here. Might even go for a crazy 18% life roll to make fishing a bit less crazy? Who knows.
4) Well I'd record your runs and test that in a good rift, if you really cap your IAS. Of course if you do, then INT is king. But I only see that happening on a crazy summoner/grotesque/maggot lord rift, and rifts are rarely single floor these days, so not sure if you want to constrain yourself so much here. You'd also pretty much gamble for Saxtris/Hamelin or leave (but you might have to do that anyways).
5) Yup, any lightning percentage is enough - but that's according to the knowledge we have right now.
6) Use a calculator for an exact answer, but probably elite damage. Life% probably depends on your vit. Armor no way, if you need armor socket rubies or get it elsewhere.