There is a good resource for making sure the tension is the the same for all strings here:
https://b0b.com/infoedu/gauges.htm In terms of octave, I have never had any problems here... An octave too low definitely makes the strings feel too slack, and an octave too high (if you can get there!!!) would certainly cause some visible strain on the tuners, I would think.
But assuming you know that one string is correctly tuned, the chart on the linked URL will help if you want to try other, more exotic, tunings. I have used this myself for different plank set-ups, but always reverted to the 'normal' C6 in the end. I figure until I get to the point where I am limited
only by the tuning, I should just persevere...
As it is, my limitation turns out not to be anything to do with the guitar!
Hope that's useful, anyway,
Sid
