Seems like I have one of the more simple setups. My Yaesu FTM-400XDR has a built-in GPS and TNC with full APRS support, the only trick has been initial testing with sending and receiving SMS messages, everything else was straight forward. About the only thing I've done with APRS outside of my radio is check aprs.fi to make sure my beacons are working. It's also handy to allow friends/family to follow our progress on trips.
That's one of the reasons I got my Kenwood TM-D710GA. I showed how to follow my route on aprs.fi so when I'm out people can see where I am. And when I get to my campsite or if something goes wrong being able to send a quick message is nice.
I also have a Icom ID-51 that I recently figured out has a TNC. I knew it had GPS but it's easy to get my location transmitting on it.
Found my son's old Android and got it charged but found APRSDroid costs money. Not worried about the $5 to pay for it but not about to give the play store my credit card since we are all Apple users... Wonder if I could pay the creator directly and get a "redemption code" that is good on the play store???
Sideloading is a bit different on each phone but usually means finding an option under the phone's settings to allow installation from "Unknown sources" usually buried in the settings/Security menus.
One bonus of sideloading over the Google Play option is that you can choose the OfflineMaps Build then obtain and install a map for your area and not need constant net connection.
I have something like Disk Commander on my droid and I load the apk on the external sd card and then through Disk Commander (or what ever it's called) I click on the program and it asks if I want to install it.