Yep, choose what you want / need (in most case this is lesser than 100 packages, but in some cases, people want stuff they don't use, so its a bit more.), and then add the repo to your installer. You can rid the other repositories (check the ones we're tracking in the other sticky) as you no longer need them. Repositry will work almost exactly as if you have the original repository, with the down side of:
1) Packages will be approximately 1 hour slower than the original repository
2) New packages doesn't appear automatically... not an issue, subscribe to RSS feed and you know when they come up, pop here (or some time down the road, web app), and add it.

You still have the option to choose whether or not to update via installer. That's something you must do yourself (unless there's a malicious package that updates other packages for you... wait, malicious? *shrugs*).