1 - To the end, with Yagluth slain.
2 - ~45 hours, although my first world had ~100 hours and I stopped just short of Yagluth.
3 - Atgeirs, 44
4 - Archery was at about 49 and was unnaturally high because I used troll armor all the way up until the plains, which made melee pretty difficult.
5 - Running 52, tree cutting 34, mining 36
6 - It varies. Hunting down & prepping for bosses it the main activity for progression, but building is also pretty fun as is stockpiling resources.
7 - I used several mods, but nothing largely gameplay changing, mostly quality of life. Things like Auto Repair, Instant Monster Drops, Crafting With Containers, Invis Helm, etc. As for tricks, nothing really notable. The only stat I cheesed was unarmed while waiting for my rested bonuses, and I chose unarmed because it has no impact on my gameplay.

I'd be curious what people think are the 3 most powerful melee weapons & why they pick the 3 that they pick.