Installing SuperSU -- I found a binary problem Hi I am following Android Central's guide to root my HTC One Mini.
I got to this part:


  After installing the Custom Recovery, Your phone is now ready to get root access!  
  
  Step 1: Connect your Phone to PC and Copy the SuperSU zip package to your phone SD Card.  
  
  Step 2: Next, Reboot your HTC One Mini into Recovery Mode, Here is how to boot it:  
  
  
  Power off your phone  
  Now Press and Hold the Volume Down+Power buttons simultaneously for a few seconds.  
  Using the Volume Up/Down and Power button, Select the Recovery option from the menu.  
  
  
  Step 3: Once booted into the Recovery Mode, Select the Install option and browse and select SuperSU zip file from the location where you’ve placed it.  
  
  Step 4: Swipe the button which says, "Swipe to Confirm Flash".  
  
  Step 5: Once it is done, Using the Reboot option, Reboot your phone.  


The SuperSU zip file is in my internal memory but when I use "install" in TWRP and click on the zip file, it shows as empty in the folder (I know it's not empty).

Can I just unzip it on my PC and place the files in the right location on my phone?

I have downloaded the app SuperSU from the play store, tried running it only to get the message "there is no SU binary installed, and SuperSU cannot install it, this is a problem. If you just upgraded to android 4.3 , you need to manually re-root &mdash; consult the relevant forums for your device."

Could there be a problem with the way I unlocked the bootloader or would I not been able to have installed TWRP if I had screwed that up too?

Only my third root and I am no pro keyboard jockey so please, an idiots guide, if you would be so kind!
There are many questions here, so the actual problem is somewhat unclear. Getting root app from Playstore (on an unrooted device) will not work. Therefore, I suspect it all relates to problematic/corrupt SuperSU zip - without it, you can't get root functionality. It is not recommended to tamper with SuperSU zip file! 

I suggest re-download SuperSU here and install it from recovery. If you can't install it, there could be other problems related to unsuccessful previous steps. Follow the rest of the steps from your guide and also seek help where the guide was originally posted. Good luck.