Thanks for the replies folks. Turns out the whole black screen thing on reboot is me being impatient while it restores the space on the new SD card.
I tried it all again from scratch with Pishrink, only this time left it for about 20 minutes after the splash screen then black screen thing. It went to the black screen as before but I decided to be patient this time and after about 20 mins or so it rebooted itself into Emulationstation as it should. Everything seems to be running absolutely fine. Thrilled to bits! Really wanted to keep this image as I'd put a lot of weekends into it!
Thanks again. :-)