Keep in mind that as far as BGA work goes, tristar is pretty easy. Your latter question is theoretically possible, but in practice extremely difficult. Try to avoid using wick on pads when you can. All those exposed traces indicate some excessive rubbing on the board.
Clean up or flatten out all the shield solder joints with a soldering iron and wick if you need it. Slip the shield back on and use an iron to solder the points again. You don't need to do a perfect job on every single joint. It helps if you try an avoid prying/bending the shield during removal.
It is likely a defective replacement part if it started happening after a screen repair. That phone is notorious for digitizer (the layer of the screen that senses touch) issues. It is even seen on original screens.
If the screen stays black because of damage or failure of the lcd, the easiest way to extract any data will be to find a shop that will plug a new screen in temporarily to get the data. In order to move data the device will have to have usb debugging enabled. If you haven't previously connected it to a pc, this will be challenging if not impossible with no image or touch function on the screen. PS if you use a google account check to see if your contacts are stored there. Most of the time they will be there as google saves them unless you tell it not to.
A red screen is typically related to a bad front camera flex. Unplug the battery, then unplug the front camera flex and home button flex. Reconnect the battery and try to boot the phone with them unplugged. If it boots fine, then repeat the process adding the camera flex and home flex 1 at a time to determine for sure if which it is that is causing the issue.