Here’s what I’ve done:
1. create a new page template (don’t call it home.php!) with all the html/php you need for your front page. Upload it on your theme folder via ftp.
2. create a new page in the dashboard using your template. Set it as home page on the Reading section.
3. I used the Login With Ajax plugin to redirect logged in user to the activity page. But any method of redirection could work.