As well as there being hundreds of individual models of Ukulele on the market (all of which differ to some degree), no they are not all the same. There are over 690 different brands identified.
More generally, there are four standard sizes of ukulele, the soprano (standard), the concert, the tenor and the baritone. Each is successively larger by an inch or two.
"Ukuleles" is a plural noun.
All ukuleles are easy to play!
You can find them all over the world. However, most agree that the best ukuleles are made in Hawaii. The quality of Ukuleles being made in the rest of the world is improving. CF Martin continues to make some of the best and they are found in Pennsylvania, USA.
Their web site does not show any ukuleles being for sale.
Standard bass Guitars, banjos, ukuleles, violins, violas and cellos all have 4 strings.
All ukuleles are strung with the 1st and 4th strings on the outside. They go in order 1, 2, 3 and 4.
One source would be eBay. Starter ukuleles are available for about 10 pounds. Real Music and Purple Turtle are a couple of shops that carry ukuleles.
no
Mahalo makes ukuleles in all sorts of colors, including pink.
There are many ways of making an ukulele. There are a few standard shapes and sizes, but a wide variety of possibilities. The quality can be a difference in manufacturing, which can make a big difference in sound.
Stringed Lute
Harmony ukuleles where made in the US. They name was sold in the 1970s to be used on Asian produced guitars.