What are the 10 Samadhis of the Avatamsaka Sutra? I'm referring to the chapter in the Avatamsaka. Here is one summary: 


The Great Samadhi of Universal Light
The Great Samadhi of Wondrous Light
The Great Samadhi of Sequentially Going throughout all Buddhalands
The Great Samadhi of Purifying the Activities in the Depths of the Mind.
The Great Samadhi of the Magnificent Treasury of Knowing the Past.
The Great Samadhi of a Treasury of Wisdom Light
The Great Samadhi of Fathoming the Adornments of Buddhas in all Worlds.
The Great Samadhi of Distinguishing the Bodies of Living Beings.
The Great Samadhi of Ease and Comfort in the Dharma Realm.
The Great Samadhi of the Unhindered Wheel.


Here is outline of the whole thing that mentions the 10 Samadis.

3 is clear enough, there is a chapter in the Avatamsaka that does this, (chapter 4 I think).

5, 7, and 8 are results of meditation rather than steps leading to it.

Were these Samadhi's something that a lay or monastic bodhisattva would be expected to practice, or are these Samadhis that an already enlightened or nearly englightened Bodhisattva would engage in?

(Sorry I don't have a link to the full text, I only know of the Cleary translation which is available on Amazon.)
My take on these kinds of lists in Mahāyāna sūtras, especially late ones like the Avatamsaka, is that they are literary devices. The Avatamsaka is a particularly literary text. It's mainly a work of imagination, a kind of elaborate, surrealist Buddhist novel.

The link appears to be to a summary rather than a translation. There's a ( illegal) copy of Leary's translation from the Chinese online here. (Chapter 27, page 811-862). A quick skim suggests that it may not give you the kind of information you are interested in.