It is going to be backlight.
You had an image produced after your install = install was successful. (The fact that it was a half screen is because LCD was cracked--this is very common).
You have no image after trying to replace an LCD----this is classic trigger for the incredibly common iPad mini backlight failure. I fix these by the dozen and sometimes it is hard/impossible to see the faint apple. Don't worry about that---this is a backlight problem for sure.
To confirm---find the backlight fuse from one of the many posted photos. Set your multimeter to continuity testing and place a probe on either side of the component---you may need to solder on some straight pins in order to get the probes to be able to not touch anything else. If the fuse is the problem there will be no continuity across the fuse.
You may also have damaged the backlight diode---set you multimeter to diode testing and measure across the backlight diode---it should show infinite resistance in only one direction, and something like 150-200 ohms in the other direction. If infinite resistance in both direction = need to replace.
jessa