Go with wafer type lights on a dimmer. dont bother with recessed cans.

Definitely wafer style LEDs for ceiling lighting. I'd put one in each corner, 36" from the walls, and another half way between along the 18' walls. A total of 6. Though it may depend on how you're going to use the porch. A couple of sconces mounted to the house wall may be all you need,

We only had sconces on our screened porch, also in mn. They were rarely used. Mainly because at night we rarely wanted lights on out there (bugs, even outside the screens, are bad... and we were usually out there to enjoy the dark, or the fantastic thunder storms). Whatever you do it will likely be more than enough.

It's a function of ceiling height and the design of the fixtures.

Fiberglass batts are not going to do much for sound.

I would not put more than 5 and that will be overkill at night, I would want a center light possibly on its own switch. is there a porch light on the wall?

My screened-in porch is similar in size (12'x18'). I have a ceiling fan (no light) and 2 can lights. It is plenty of light. As someone else mentioned, we rarely use our lights. They attract too many bugs to the screen and detract from the ambiance of being outdoors at night. I'll turn them on to find/grab a blanket and then turn them off. I'm in TN and use my porch for 3 seasons, too.

We have a ceiling fan ( no light) and lamps. It is surely personal preference. We prefer the ambiance that lamplight creates. We do not want to feel like we are in Walmart 🙂.

We live on a wooded lot in Pennsylvania, and we can still get some very tiny, annoying insects. We actually rarely turn any lights on. We enjoy watching the animal activity outside without the neighbors seeing us in our jammies.

We used to have a breeze way with an attached garage garage and the touch garage on the outside but in the bruise way had a light bulight but what we enjoyed the most was the LED lights elites that ran they were called rope lights and they ran the upper part by the roof all the way around the porch