WillC said:Most succulents will stay very small.
Not true. They cover the whole range and there is no general rule like this.
Your Graptopetalum will be small for only as long as it takes to sprout new heads and spill over every available side of the container... not a great long-term choice for a space-constrained garden. They are amazingly good at overflowing a small container. You can start them from leaves and for a brief while (weeks) they will sprout a miniature plantlet, which you can enjoy in a very temporary way. But the future looks like this:
Tiffany pointed out a helpful link. Lithops are a great choice size-wise but a really bad idea for a beginner plant unless you're willing to subject yourself to great discipline when you water (and grow any other plants in the container the same way, which can lead to their downfall).
A lot of small plants will branch profusely, thus end up not so small in the long run. As long as you are aware of this behavior, you can nip the excess growth in the bud. Crassula tetragona is often used in miniature gardens because of its miniature tree-like look... it will outgrow a small container and reach about 2 feet tall, but can be limited by size and serve for a while in a limited space situation. Mammillaria elongata is another choice which will look good for a year or two and then start to sprawl and take over. There are smaller Mammillarias but these cacti are demanding about light and not likely to do well indoors where it may be limited. The more light you can provide, the better for these plants in an indoor situation.
The main issue with the micro succulent gardens I have seen is that people set them up in terraria and the like where there are no drainage holes at the bottom to let the water out. It's possible for an expert to grow plants long term in this kind of set up but well beyond the reach of normal folks. The issue relates to rot where moisture does not have a chance to exit the container, and salt buildup from repeated watering over years of time. So look for a container with an exit hole if you want to keep a micro garden going for the long term.
