Full BoM for my early specs below.
Debating if I go with 3xAA NiMH or 1x LiPO. There are pros/cons to both approaches. If I could find a water proof 18650 battery holder + leads I'd go that route as I could add a battery meter.
For waterproofing: I'm going to be ordering some of the moldable plastic play-doh stuff for wrapping the sensor + esp32 to make it water tight.
My current indoor build is coming along really well and I have the core pieces/parts sorted out for the firmware side. The indoor build is using an esp32 and >1 senor with an i2c mux so the outdoor one with a single sensor should be much easier to put together and cheaper as it won't have solar or display.
Given all my plants can see my WiFi at home I'm going to be going that route for now. If/when I need more distance I'll likely build a LoRa gateway for them. Unfortunately that opens at a much higher cost to do "right" and I'm not there yet for needs.
Soil Sensor: https://www.adafruit.com/product/4026
Temp sensor: https://www.adafruit.com/product/381
Battery Holder (AA): https://www.adafruit.com/product/771