14-18 ft/lbs. No specified torque pattern, so just go in a criss-cross pattern. Nissan service manual says to replace the gasket. If you have to re-use it, I would at least coat it with copper spray gasket.
Lower the trans but leave it attached to the engine and as you jack the trans up, you will eventually get it at an angle where you can partially install the dipstick tube. Continue to raise the trans and it will eventually go in.