The dipstick hole looks rather small. Would I still fill this with ATF?
No you don't fill it. You bring the car up to normal operating temp by driving it around for 10 to 15 minutes, then you park it on a level spot. While the engine is running, trans in park you check the fluid. There should be a cross hatched or a min - max area on the dipstick, your fluid level should be in this area. If not add a little & check again. Remember if the fluid is showing a little low on the stick, it wont take much fluid to bring up in the full range. The trans dipstick tube should be about the size of your finger. The oil dipstick tube will be about the size of a pencil.