No expert on this but with a bit of googling you can find all your answers.
If your box is stalling all the time, give it a clear out, reflash a new image, delete unnecessary plugins and media plugins. Keep it barebones, your box will fly.
You can have 2 boxes, but use 1 satellite line. You can then use something like the remote channel stream converter plugin, to import your bouquets to another box.
As you only have 1 satelitte cable, you will only be able to watch channels on the same transponder at the same time.
If you want to watch different channels or record and watch a different channel you would need an lnb with at least 2 cable lines.
As for a central recording hub, you just need a nas drive on your network, and then you set up your recording to save to that.
For zapping speeds, you don't say whether you are using a paid line or other, but usually this is down to your provider, the speed of your box, the softcams software you are using. I suggest using oscam as your softcam software with a couple of lines. If using any other softcams probably best to give your config files a once over and remove unnecessary stuff like logging.
I am using a hybrid enigma2/android box at the moment and to be honest I find the android side of things annoying. I stick to enigma2 most of the time.
If you want to use your android boxes, probably best just to use for iptv, stick perfect player on them and get a couple of descent iptv lines.

