'Recycling' off-the-shelf Android devices as server ('Toaster-Net')

Since Android devices tend to be relatively low-power un*x devices, this seems like an obvious usage, I was already able to run the basic setup of what I had in mind, but I think it's a right time for me to consult about this. I have a few unused Android devices (tablets and phones, some with a broken display), I've seen there are several ways to install various Linux distributions on them, installed some scripting environment (Node.JS or Python) I've successfully ran a few that did not require rooting, and I've ran some server software from them (like Node-Express based REST etc) I'm left with the following open questions, maybe there are much simpler solutions to this scenario. I'd be happy to hear of such a usage scenario. 1. All these non-rooted Linux apps I've installed - were running as long as the device did not go to 'sleep', I've tried several 'insomnia' apps, but actually non of them worked correctly, and they were all trying to keep the Display awake. I would actually prefer the Display to be Off, but the device to not sleep, is there a scheme for that, or is that not the general design of a common off-the-shelf Tablet let's say? 2. The app seemed to randomly go into 'background' even with the display on; Is there a settings to prevent that, so that I would have a reliable HTTP listener? 3. I understood that Battery life / performance - might be deteriorate severely - by keeping Tablets Changed 24/7, is there a standard solution for that? I've seen some recommendations for rooted apps that prevent charging on and off, but lacking another solution - a timer-AC-mains-Socket can be installed Generally this seems like an ecological idea for 201x style ARM based Toaster-Nets; I found that I often need some 'cronjobs' to run and serve some not very CPU demanding experiments. It also seems like a good exercise in local net setup; I can see this setup being used in schools for example to provide students a network they can play with and setup web-apps. If there's a proper guide for this anywhere, please point, I've seen good guides for how to install Linux / a similar setup - on your phone for example for 'on and off' usage, but nothing that covered the actual aspect of leaving a bunch of these machines as a small server-farm. Thank you!