You wouldn't be able to download everything. You would have to point the webapp to local data to get the speeds you want and obtaining all of it, especially for mapping software, isn't trivial. Doing this would be more or less similar to hosting something like a Runescape private server. All that data that the game uses has to be recreated locally because it can't all just be scraped. That's why you don't see 100% authentic game private servers out there.