OK, I've done a (very small) amount of reseach into the points raised.

Firstly, the concept that the pyramids were surrounded by water seems unlikely. The Egyptian desert is not a good place to maintain pools of water and all the references I have found are of a ceremonial nature. The primordial mound (the land) was believed to have risen from the primordial water (the sea) and the pyramid is a representation of this mound (the ben-ben). The milky way was regarded as a celestial river equivalent to the Nile and it was part of the funery ritual that the dead pharaoh was carried by boat. The pyramid texts show a depiction of a funery procession in which the boat (complete with oarsmen) is being dragged (on dry land) by a large number of men pulling on ropes. There are boat pits around some of the pyramids in which such boats were buried, presumably for the pharaoh to use to navigate the celestial waters. These burials are not consistent with a pyramid that was surrounded by water.

Secondly, the similarities that you present between Silbury, Marlborough Mound and the Djoser pyramid are somewhat coincidental. All stepped pyramids by their very nature have flat tops and since there are quite a few to choose from it's easy to select one that just happens to have five steps. The "steps" on Silbury are small by comparison with Djoser and may not be an original feature of the hill. Essentially Silbury is conical whereas Egyptian pyramids have square bases.

Thirdly, you mention the time frame of construction. It's true that many megalithic structures were being constructed around the world during the Neolithic and Bronze Ages. Mounds and pyramids are the only way to achieve tall stable structures without the use of reinforcements like steel. I have no idea why these distinct groups of people should choose to "build big" at around the same time, but the fact that they did is not in itself evidence of cross-cultural communication without other more compelling evidence, such as foreign artefacts.

Lastly, we have the Kennet/cunnit linquistic "connection". I'm by no means a linguistic expert, but there are a few points that strike me. Firstly, the word may have origins that go back way before either culture. Secondly, the Egyptian texts were written without vowels and it is only by convention that certain vowels are attributed to certain words. Thirdly, there are similar words that may have entirely different meanings. If someone were to find an Egyptian artefact in a British Bronze Age burial then I would say that your linguistic connection was highly likely, but in the absence of this it just appears to be coincidental.

I'm not ruling out the possibility of some cross-cultural communication, but I think such different cultures would have regarded each others artifacts as exotic and would therefore have exchanged goods at every opportunity. This should give rise to at least a few items that are out of place in the archaeological record, but to my knowledge none have been found.