if it scans, then this indicates that the WIFI controller is working fine. But not picking up signal shows the antenna is either damaged or unplugged. To confirm this try scanning again with your device on top of your router, it it picks it up then it's an antenna problem.
The right hand side of the screen is where the cables plug in. It's also where the Shield doesn't like to sit flat on the screen. It's not due to the battery as the screen would be lifting on the left hand side. But the LCD shield is very common to not go on flat when replacing it on a 7/7P/8/8P. Pull the screen off then take the shield off. And really take your time getting the cable under the shield to sit flat so it doesn't push the shield up. This is also a common cause of a yellow spot where the shield and cables meet.
I would check your charger. What you describe sounds like an extremely flat battery. Plug in a different charger that you know works and see what happens. Otherwise you may have a problem with the charging board or circuit
Not a software fault, definitely hardware. Sounds like you may have caused more damage when you replaced the screen yourself. If you know anything about board repairs, id check the backlight circuit on the board. If you don't, take it to someone who can do micro board level repairs.
If you mean spinning as in like you are turning the phones orientation all the time then sounds like your gyroscope is faulty. To confirm this, open up your phone dialler, dial *#0*# and select sensors.
there are 2 different types of ipad mini digitizers. there is one that comes with the home button pre attached and pre soldered. There is one that does not come with the home button, this one need to be desoldered from the old digitizer and resoldered to the new one, if you haven't had experience doing connector soldering or micro soldering before then you would be better off sending it back for a refund and getting the one with the home button pre soldered.
sounds like you replaced a board with a simple Backlight or LCD board problem, with a board that also has a motherboard fault. Take them to someone who does Micro soldering and you can get them fixed and have 2 working ipad motherboards