How do I avoid re-entering administrator password when I try to remove apps with Finder?
Well, that only happens if you try to delete the App from Finder, which is not they best way in my opinion.

If you have downloaded them from the App Store you can go to the Launchpad and click and hold, kind of like deleting apps from iPhone, and apps will start shaking and a cross icon will apear on the top-left of apps that can be deleted that way.

Personally I use AppCleaner as this software also performs a search for other places where the app to delete may have stored data and gives you a preview for you to review and confirm deletion.

I do some development and when I want to emulate first-time installation process/experience I use AppCleaner to delete any profile or history data stored outside the App Bundle.

Finally, you can delete apps from Terminal App but I won't provide details as this is not recommended even if you know what you are doing :p.