Congratulations, you have really accomplished a great deal since June! I think you will find HF very interesting, despite the poor band conditions on 20 meters and up right now.
You'll still be able to make contacts once you have an HF antenna up that allows you to transmit. A simple G5RV dipole, fed with 450 Ohm balanced line to a small manual tuner (or external automatic tuner) can be a good way to start. It will will tune all bands reasonably well and get you on the air. The overall length is 102 feet. You can make it or buy one.
It can be configured to use coax after the balanced line, but I've never built it that way. Just run the balanced line to the tuner (with a balun inside it), or put a balun outside the house and bring a short length of coax in to the tuner. Same in a mobile / portable setup.
That 7100 is a nice radio and a good choice for a first radio, should serve you well. You will want an auto tuner for the antenna depending on what you are trying to match to on HF. There are many choices, and even starting with a manual tuner will work. You'll learn some things twisting knobs!
A vertical can be another way to get on HF, especially if you don't have trees available to hang wire antennas from. It can be for one band, or multiband, or a single spike and a matching network for all band use.
Mobile HF antennas are whole other world of possibilities. Mobile HF is fascinating, working DX or contests from a mobile is fun.
Having Winlink for e-mails can be a way to stay in touch when beyond cel texting range. I was fortunate to find a Pactor modem for HF Pactor Winlink which will work from anywhere. That is one of my next radio projects for the RV. It also supports HF Pactor APRS when away from any VHF APRS nodes, so tracking your location anywhere is available on www.aprs.fi , the same as when using VHF APRS tracking. Just long haul capable on HF when remote.
I have a feeling you are well along and probably have a plan for antennas in mind. Sounds like the next step....
