When you run out of uses for your smart phone you can always convert it to a wifi LAN camera using IP Webcam by Pavel Khlebovich and consume the output in VLC. I have been using an old phone for this purpose successfully for years.
I had the same plans, but I was always afraid that running the camera for a long(-er) time will degrade the sensor fast, so te phones are collecting dust in a drawer now :)
There are enough settings to allow for just about any use-case. For me, I had issues doing full HD over wifi, since the router is upstairs in a different room, but you can play around with settings for resolution and FPS until you find something stable enough for your setup.
The heating seems okay, leave it on 24/7 with no downtime. Occasionally the phone falls off the wall due to the advanced taping mechanism keeping it there, but that's not the software's fault.
You can have it automatically run at boot. We have load shedding here often, and the phone recharges quickly enough after the 2 hour shutdown of power and can stream throughout (connected to mobile hotspot wifi - also for loadshedding reasons)
I don't buy many apps, but this one I recommend for sure.
Note that I have no specific knowledge on the subject ; it's quite possibly a fear without any reasonable ground.
But I had a cheap speaker that I used with a Chromecast audio to listening to podcasts ; I left it always on and... I came back just in time one night, the speaker was producing a large dark smoke.
I almost put fire to one of the oldest habitation building in Paris (1704) - with a lot of apparent wood etc. :-(
Not proud of it, but good lesson. I recently read about the risk of fire in cheap replacement phone chargers. Google's ought to be of quality but... still a no-no for me.
Obviously, advice from people with knowledge on the issue will be appreciated.
Having it plugged in, OTOH, probably doesn’t matter. There’s safety IC to prevent overcharging. Actually fully draining, mechanical damage, water damage etc. are more dangerous, which can happen during normal use anyway.