OP, 40 something woman here and for me it's the Crème de la crème. Congratulations on finding someone who will do their job properly. I was once called "shitty" on MN because I said I would not have sex with someone who would not go down on me. But my body, my rules!
Body size is not relevant, if someone is into you they are in to you. Oral or no oral, you don't change size.
Positions: Go for what feels comfortable for you. For most of us, comfort and sex go hand in hand. You might find putting a pillow under your bum helps when laying on your back. If you are comfortable with him you should be able to gently position his head gently for your ultimate pleasure. It sounds as if he would be happy with this and only you know what sensations you are getting.
As for duration, it is down to you and your needs. It's possible that after climaxing from oral you find yourself ultra sensitive, almost to the point that you cannot be touched. If you prefer to stop at this point, then do so, but if you can ride this, the yellow brick road is just around the corner.
Wetness is healthy. As for taste, I would describe myself as past the curious stage and I assure you that there is nothing remotely unpleasant.
Enjoy yourself. x