OK - makes sense.
I just think you'll find it increasingly difficult to find decent lights that don't charge via USB.
For the rear, it sounds like you won't be a heavy user, so I'd go with the suggestion of replacing the reflector with the relector/light combo that is available.
There is quite a cheap option for this, but the name escapes me. I believe it may also take a little fettling to fit correctly.
Personally, I think a light that low down is too low for traffic (and I've had that conversation/argument in the past here) but others disagree. After all, it's where Brompton mount their hub-charging lights.
Then you could use the one you've bought, mounted high-up on the seatpost in conjunction with the lower one in place of the reflector. In those instances where a coat/saddle bag would obscure the top light, you'd still have the lower one.
If you do a search on the forum, it might bring up the one I'm on about. It looks almost identical to the current reflector, but has lights in it too.