My main tip for someone setting up their box is get the remote app. For the Shield, definitely download the official Nvidia Shield remote app on your phone (there are Android and iOS versions). It gives you a mouse and keyboard and also shortcuts to apps, among other things.

There is also a Google Android TV remote app that can be used on your Mi Box (and also the Shield but the Shield app is better for that) but I don't have a Mi Box so can't comment on how well that works.

Having the remote app keyboard in so much easier when setting up your accounts for various services. And the mouse if very useful if you use a browser. You can sideload Chrome if you want a browser and use the remote app to navigate it. There are other browsers too but that's what I use. This is on a Shield. I don't know what you can sideload on a Mi Box.

Download a file explorer from the Play Store. I use X-plore. It has all the functions most people would want.

Some popular free TV apps (with ads) are Pluto TV and Xumo. If you have an antenna and tuner you can use Live Channels for over-the-air TV and free DVR. If your local library supports it, you can get Kanopy for free with a library card or maybe Hoopla. Check your library website. The CW app and CW Seed app are free if you watch any of those shows. Some shows are free on some of the major network apps. Several paid services also have free trials in their apps.

If you have the 2019 Pro version of the Shield or any of the older Shields, you can use it as a Plex server and load all your media to it.

I don't use IPTV or VPN and just use the stock launcher so won't comment on those.

For iptv, you can try https://worldbestiptv.org/en/

The best launcher would be nice too.