I looked at your recommendations when provided, but was busy with other things so forgot to reply. I now have 3 systems of sensors reporting to the Uno (Blueline power meter reader, Acurite 5n1 weather station, Acurite 592TX temperature sensors (1 currently, but up to 3 channels))and will be adding 1 or more local sensors to it as well (barometric pressure currently, but probably temperature also at a minimum). I have all of this sending data to the RPi via MQTT and am working on optimizing the location for the Uno for best reception/least packet loss. I'm also planning on tracking UPS performance as well as RPi CPU/memory.
That being said, I looked into emoncms again this morning and it appears that the data is stored on the cloud somewhere. If so, that's not ideal due to reasons I originally posted. I thought this would be the option I would utilize until I saw that. I've looked at Grafana/influxdb and they look great, but it will take more effort to figure them out. I decided against freeboard since I specificially want plots and not gauges.
I considered using rrdtools, but it looks like it's only capable of storing at a single frequency and then purges anything over a certain age (maintains a certain database size and loops to overwrite the oldest data next). There's a number of tutorials/guides, but I haven't found one that's a close enough match to proceed. I have a working HA server at the moment, so I'm leery of installing too much and risk corrupting things. When I do proceed, I'll certainly back up the SD first!