Another welcome. Your "cottage" looks like a palace to me. I live in a trailer which is not much more than an old fashion bread tin but plenty good for me.
As far as a beach goes, I put in a small one (about 25' wide). I have lost some sand to deeper water but the pond is 10 yrs old and there is plenty of beach left. A 5 to 1 slope puts you standing in 5' of water at 25' from the waterline. In my opinion a beach is a great addition to a pond. On a very hot day it is nice to be in chin deep water without having to put out any effort or using a flotation device. Also a whole different little niche for lots of things. Research beach building, there are ways of preventing the sand from shifting.
Think EVERYTHING through thoroughly and do lots and of lots of research.
Good luck and keep us informed of your progress. Take tons of pics. Guy named Bretski did a similar project and documented it very nicely. Perhaps someone will post the thread, definitely good info for you.

Do nature a favor, spay/neuter your pets and any weird friends or relatives.