So what I should do is first test the incoming 4g signal. If that's low, I need an antenna, or something to improve it. Do these devices typically have a gauge to show signal strength, like a phone has? If I then have an issue with Wi-Fi, then I need something to improve that, right?
First, you need to figure out if you have any signal by the carrier. For example, in our parts of WV US Celluar is it (Verizon rides on US Celluar towers).
If your signal is flaky, you need to figure out where your nearest tower is and point to it, or get as clear line of sight as you can.
Second, you need to determine how good your signal is. Sometimes devices have bars, sometimes their modems have bars when you log into it. Ours had near 0 about 100 feet down the hill where our cabin is, and very good reception on top of the hill. I had experience with signal boosters, but the one i had was a 2G (phone) booster, so I got an antenna for the modem. I almost returned it as the signal barely improved.. but my bandwidth (download speed) did improve even though it was still showing nearly 0 bars, plus I almost never disconnect, so I kept the antenna. I test my bandwidth with speedtest.com
Basically, the higher in the air and the less obstruction it has (trees, mountains) the better your signal (and bandwidth) will be.
While I considered building a solar-powered hub on top of my hill, adding an antenna on top of my house was good enough. I use 4G as my backup link (for DSL), as I am capped to 20 or 40G monthly on my $40 plan, but it really works rather well.
For those of you in the boonies, there are also long distance WiFi providers that might be able to service you depending on elevation. I used one of those services for a few years, but my DSL got sufficiently reliable. Try
Search All Internet Providers by Zip Code | HighSpeedInternet.com. These are usually very regional/local providers, they won't be affiliated with AT&T or the like. Mine was/is called wave2net, I am sure you never heard the name.