Tranny Dipstick should already be in the dipstick tube (?).
Ams synthetic will be fine (cross check compatibility on package)
'Be careful about cleanliness when you r+r the pan to replace the filter.
No DIRT anywhere.
EDIT:
It will not offend the tranny if you run it through an under car wash before the surgery.
I'm such a nutcase I'll spray the underside of the tranny area with a
degreaser; brush and rinse (and then inspect) before the work!
'Observe correct torque on the pan bolts upon re-installation.
(hint: finger tight...then cross torque...working outward from the center.)
Use a new washer (if called for) when re-installing the Torque converter
drain bolt.(again correct torque applied)
'New washer on the pan drain bolt (if called for) [torque]

"Dex" is just a description of a certain type of ATF's specifications.

When you refill do so on flat/level ground (makes checking fluid level easier).