Yes, they will be for life.
Will probably settle for one then.
Defitately agree with that!
I will most likely upgrade the tank but not sure when so not worth risking at this stage.
What about a catfish like a Raphael or Bristlenose to pick up all the wasted food?... ... Or am I defeating the idea of a 'wet pet' setup?
You can get the BPs later if you decide to get a 180g (good plan on your part).
GT's will scour the bottom for food, and can be endless garbage disposals, so no need for a bottom feeder unless you really want one. Bottom feeders need love too and should be fed appropriately, and not regulated just to scraps.
GT's tend to produce longer "strings" of poo than other cichlids, which suggests to me a diet with aquatic vegetation is really good for them. I would add rotate in New Life Spectrum Algaemax due to high algae (aka veggie) content to your regular pellet choice.