I am serious with it of course!
The a few additional points you should consider:
1) you'll better use your own website to advertise and provide downloads for your game.
If you're uploading it to some general service provider, those can block access to the download (and get you into a lot of trouble with your customers). That happened to several people on this site in the last few months who had used a free image hoster for tutorial pictures, or for script hosting - and because too many people downloaded them, they exceeded the free bandwidth and got their files blocked.
Your own website would also solve your problems on how to contact customers
2) Most professional people that provide demos today make the demo different from the main program
Yes, that will require your customers to redownload after purchasing, but if the later part of the game isn't in the demo, then it can't be cracked from there.
You might even think of making the dome something else than the beginning of your game - a demo is to provide a good view of the best game aspects, and very often the beginning doesn't give the player full access to all game features as he needs to learn them one after another.
It's more work for you to make a demo with a side story than using the main story, but usually that is better than risking your main game to be cracked.
3) Bughunting and Playtesting are extremely important for first commercial games
If you're new with publishing a game, then you need to make sure that there are no bugs inside and the game is playable.
Because if your first game is bugged, you'll never be able to sell later games due to having scared away all customers with your first release.
And that means you have to get at least half a dozen different players to play it half a dozen times each, just to check that there are no obvious bugs in it - consider several months a minimum for bughunting and balancing, before publishing it.