Visited in early November 2012, and the interior was being refurbished, with scaffolding covering must of the interior, so difficult to see much.
The mosque is indeed large. When I visited, there were very few people there, so hard to get a sense of how many people could fit. My guide said 200,000 people had filled it previously.
My "guide" walked me around to the different areas, offering a little history, and answering the few questions I had.
If you know you will be visiting Jakarta again, you should wait until the work is complete. Then the place should shine.
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