Chalk & cheese - the ThingsUno uses a Microchip LoRaWAN module (RN2483) to handle the protocol, LMIC is software that actually runs on the main microcontroller. This may not be relevant right now, but may come as a surprise at a later date if you need to move to a different board.
Using DevStatusReq & making up your own ADR may feel like a good move, but anything that increases transmissions on these frequency bands impacts all users.
For a newly deployed node, you need only transmit battery voltage once in a blue moon or if there are any substantive changes. Only near end of life does the battery status need to be more frequent, the irony being that could speed up its use, but as you already have a ballpark figure, you only need send a single byte (or less) in your uplink.
The ADR scheme is already well thought out and there are other potential schemes - including turning it off if the application server knows the device is being heard by two or more gateways with good reception. See some thoughts on this here: TTN linkCheck command - #4 by descartes