The default Mac applications that come with your new Mac work well enough, but they lack certain features you might be seeking. You can change your Mac’s default applications with the instructions here.
Just about everyone uses an administrator account for their primary computer account. If a malicious program or attackers are able to get control of your user account, they can do a lot more damage with an admin account than with a standard account.
The Mac App Store is truly bad. If it was just third-party software, the Mac App Store would be laughable. Why is the Mac App Store so bad, and what’s keeping Apple from making the Mac App Store better?