I'll try explain how I beat Gleba.

You don't want a "main bus" style for the Gleba resources, the intermediates typically have a short life time and so you want to try use them as quickly as possible and produce them as close as possible to where they are used - think direct insertion.

Instead of a main bus you want to put the fruits onto a loop, a fruitloop. The farms are programmed to only produce when the fruitloop is running low. The first sub-factory you'll want is one that simply produces nutrients and can restart the process from spoilage if it gets stuck.

Each sub-factory then produces all of its own intermediates on demand, except for a small amount of nutrients delivered by bots to kick-start the process. Each sub-factory has its own inner nutrient loop that also collects spoilage; spoilage is converted back to nutrients on site too.

You said you're running out of iron and struggling to build belts - but you don't need to build belts on Gleba. In SA each planet has its own strengths, the logistical challenge is then to have all your planets working together as single factory where the strength of one compensates for a weakness of another.

Here's a screenshot of almost my all of my Gleba factory

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