Why go to L4 or L5? They are very distant and require a lot of energy to reach; besides, those Lagrange points are not that stable; you'd still need some kind of energy to remain there. You'd need to orbit around those points and then, it would be stable. But this means orbiting around void.

Here's my reasoning:

In order to grow plants in space in the most efficient manner -and probably least expensive- we need to use sunlight, not artificial lights. Low-earth orbit is not satisfactory since the sun rises and sets every 40 minutes. A moon base is also not acceptable since there are 2 weeks of darkness every month. The L4 and L5 points of the earth-moon system, each at 1-lunar-distance from either earth or the moon, provide almost continuous sunlight except for a few hours once a month when the earth eclipses the sun. These should be the ideal positions for a space colony to use sunlight to grow its various cash crops.

Plants are the ultimate assembly machines. They do not break down like machines or require metal-formed parts. All they need is sunlight, carbon dioxide, nitrogen, and some water. These are very basic compounds and are easy to transport. I think it would be more expensive to support machine-based systems. Plants should be used first to provide cloth fibres to weave airtight fabrics. These would be used to build bigger orbiting greenhouses to grow bigger cash crops, to build bigger greenhouses. Eventually you would have the infrastructure to start growing enough food to feed a good sized crew indefinitely. You would finally have a truely permanent human presence in space.

Airtight fabrics are currently made by interweaving polyester with a conventional fabric such as burlap, and then laminating it with a rubber-like polymer. Plants have been used to make polymers but research has shown that the process is more energy intensive than other methods. So this is a sticky point: How do you make an airtight fabric without a really complex and intensive process? This should be the focus of research somewhere, by someone (I am sure it is).

Airtight fabrics can be cut into standard sizes and stockpiled, or assembled into complex inflatable structures. Two separate sheets are typically just fused together with a flexible resin. The two areas are then overlapped with pieces of fabric that are sewn in place. A good example of how this could work in space is joining two spacehabs together. Two balloons would simply be brought together with a hatch-sized sheet of glue between them. They would be melted into place, sewn together, and then a hole would be cut through the middle of the melted area. Voila you have a spacehab twice the size as the original!

Use sunlight to slowly electrolyze special solid compounds to provide atmosphere and then feed in some light-pipes. Set up your rows of plants and in a few months harvest. You're set to start making more fabrics for future additions to the spacestation.

A few foreseeable problems:

1. Process to achieve airtight fabric without plastic?

2. Can meteorite shielding (Kevlar-Mylar-Nextel foam) be manufactured with plant fibres too? These do not have to be airtight. The greenhouse might be off limits to human personnel without spacesuits due to lesser protection from punctures.

3. Still need supplies from earth, such as atmospheric gases (nitrogen & CO2), hydroponics, light-pipes, airlocks, fabric weaving & laminating machine.