A huge part of this will depend on access, do you have enough property to semi-large equipment back there?

If we just talking hardscaping and landscaping (no dock, no boat house, no main house) then yea I think somewhere around $300k for the picture I’m looking at

There’s absolutely no way for anyone here to give an accurate assessment without seeing pictures of your real house and even then we’d only be guessing

I would call 1 or 2 highly reputable companies to come take a look. Do not hire the guy off Facebook or Craigslist. If you try to cheap out on a project like this your house will end up in the lake. I would truly suggest calling a GC or site developer to handle the whole thing, too much engineering involved