Will it fit a coat over it?

Yes, it is possible but it should be a roomy coat of course.

Are these hoodies actual heavyweight? and if so how are tgey?

You can see through the fabric.. so def not real heavyweight

Does it shrink in washer and dryer? Do I need to order a size larger?

I don't buy or own clothes that require special handling as far as washing and drying. I found it with no precautions applied, this sweatshirt shrunk a full size. The other thing to understand about these sweatshirts is that they are big around and on the short side. I'm 6 ft 2 and weigh about 200 lb and I bought the extra large. After washing it I find it to be too big around and too short. I would estimate that after being washed, this sweatshirt would fit somebody that is about 5 ft 8 and 240 lb.

I am 6'4" tall & 225lb weight. Will size XL suit me?

My husband is just over 6’, 200# with long arms and the large fits him comfortably. He feels the XL should fit you unless you have a long torso and arms. Then order a tall.