Hello, one thing that I saw was wrong is your placement of the edits. (there may be more, I am not a pro)
It should look something like this.
<key>Boot Banner</key>
<string>No</string>
<key>GraphicsEnabler</key>
<string>Yes</string>
<key>Instant Menu</key>
<string>Yes</string>
<key>IGPEnabler</key>
<string>No</string>
<key>Kernel Flags</key>
<string> -f cpus=1 npci=0x3000 darkwake=0 </string>
<key>Legacy Logo</key>
<string>Yes</string>
<key>UseKernelCache</key>
<string>No</string>
All edits are done below the "key" and in between the "string." A space can be added at the beginning and end, but not needed.