That's an awesome idea,
Gordis!
Ok, now to Beorn's size. I know it sounds incredible that he was this big, but don't be so sure that it was something special really. Now, we know that the men of the mountains he probably descended from were related to the Woodmen, the Eotheod and the Bardings, meaning they all had ancestors in some distant House of Men from the First Age.
However, in Tolkien's works Men are not always what we regard as Men. There are Hobbits as smaller variant and then there are the Giants, a very weird race that appears to have lived in the Misty Mountains as well and who were (I can't the original quote for now) a larger version of men, just like Hobbits were the small one. This is how Tolkien refered to them, still men. Now, although in other early writing (BoLT) Tolkien regards them as evil and creations of Melkor in the Hobbit it appears that nice Giants do exist, as Gandalf wants to find one to block the entrance to the Front Porch.
This means that giant sized men did exist, they were there in the Hobbit, so Beorn's size was nothing really special.
Pure speculation on my part of course, but what if some predecessor of Beorn fell in love with a Giant and then... you know... Beorn inherited some of the Giant's qualities... more or less like Hagrid.
Unfortunately we learn nothing new about Giants in LotR, the only hint given is when the Fellowship hears voices when trying to use the Redhorn Pass.