Hi Valachio, I’m glad it helped 
Also, yes those textures will work very well in Unreal Engine 4 and I am currently in the process of including them into my “Organic Nature Pack.” Which will have some other goodies in it as well! 
Yes I agree, 64/128 should be perfect for the assets. If it is a flat wall with no extra geo I would say 64 should always be good and only for the large and more complex assets go up to using a 128.