Greg your setup is very similar to what we have been running for several years, using Trimble Mobile Manager (TMM), R1 and R2 GPS and using the cm level high accuracy via internet connection when using the R2. Our mobile field units all have cellular capability, and this enables access to the RTK corrections via internet. Our connection to the correction signal is similar to your ODOT connection.
To use it without a subscription to a satellite-based correction signal, you must provide an internet connection somehow, either through the cellular enabled tablet, a smartphone hotspot, or a pocket style cellular hotspot. In addition to the correction signal, TMM needs to login check your credentials while starting up, though Field Maps now does this behind the scenes. The R1 unit doesn't need the correction signal or TMM at all, but you still need the internet connection to display your maps on the mobile device.
For disconnected editing in areas where there is marginal or no cellular signal, you will be limited to sub-meter accuracy via the R1 unit, if you don't use a satellite-based subscription service for corrections. Yes, this is the catch-22. Preparing for disconnected editing means downloading the needed data to the mobile device while you do have good internet connection, then resynching only when back in good cell service area or risk losing your collected data. Surveyors are able to overcome the "no cell service" limitation to high accuracy work by setting up a separate GPS base station at a known fixed location, then transmitting correction signals from the base station to the rover station via radio signals. More complicated and more expensive equipment but doesn't rely on internet-based corrections.
Hope that helps.