[Bitz]

These are the very risky behaviors based on my experience.

• Botting 24x7 with no breaks, regardless of what you're doing.
  
• Teleporting. My accounts that have abused it seem to be OK if they're not logged in a few days prior to the ban waves that occur on the 3rd Wednesday of every month. (Your mileage may vary.)
  
• Fate grinding, most notably if other botters are doing the same fates. The "escort" fates are especially good at making bots look conspicuous.
  
• Gathering for long periods of time if you don't have a Discord addon to respond. Other players seem to view anyone else that is gathering as competition, and file reports if you don't respond to /say chat or direct tells.
  
• Crafting the same items repeatedly for long hours, even if done in your own house/apartment.
  

Because the open world is so risky, it seems a lot of botters are now moving to instanced botting.  (i.e. dungeons)

All accurate. Though my rule with respects to Teleporting is to never touch it. 

I stick to somewhat manageable sessions of 8 hours maximum (mixing activities up) but my understanding is that play session length doesn't matter at all.