Last weekend, I was able to complete the excavation of the trench to bury my underground ethernet cable, and bury it underground. A week later, everything is still working well and the guest house now has fast, reliable internet!
At the guest house, I added an additional junction box to deal with extra cabling so there is some slack in the buried cable, making it less likely something will go wrong if the buried cable shifts position due to the freezing thawing cycle.
Once the cable was buried, I used the dirt I had dug up to bury it, and resodded grass with the grass I had ripped up.
Ultimately, I was able to get this knocked out in two days for about $200 worth of materials. An electrician had quoted be $2200, so this was a true DIY success.