How many are there?

Where is the next one?

What type of people live there?

Who is running it?

Is it somehow connected to Earth?

Too many... such to the point that it made even the insectoid-being shudder at the thought.
The next-closest to Earth in terms of physical-proximity probably fluctuates due to orbitational-cycles.
All kinds of «sentient» beings have been enslaved; watch some isekai-animé to get possible-ideas.
For at least our neck of the galactic-neighbourhood it would seem to be mostly authoritarian-reptilians.

The rest of this whole entire universe is actually connected to earth in a way that is more of a psychic-connection as opposed to connected entirely physically; this universe itself (earth in particular) has a particularly unique-property in that it is linked/connected to multiple different dimensions/universes that would otherwise not interact nor ever interact with one another due to how they are «separated» by their own frequency ranges (something similar to how the different rooms in a mansion are separated by walls... metaphorically speaking). The other-realms range from high-vibrational-states of creativity and freedom all the way down to the lower-vibrational-states of depravity and authoritarianism.

The connection is mostly psychic, and, people who are full of negative-emotions who learn any new wisdom here on earth whilst still flesh-embodied also pass down their knowledge to many of the other beings of the lower-dimensional-realms who are also resonating (vibrating) at the same lower-level emotional-frequencies since the beings of those darkness-realms are connected mentally into numerous earth-people whose emotions are similarly negative. One who operates at a high-level vibrational-frequency who learns new things isn't going to «reach down» (psychically) into the «psychopath-filled» realms since it would require a literal psychopath to actually bother to learn (or be forced to learn via rehabilitation) before the other «psychopaths» within the realms-of-depravity have a «chance» to even «hear» of any «wisdom» that may be being communicated here on earth via the MIND of the earth-embodied sentient-being (for there is otherwise typically NO «truth» nor «wisdom» existing in any of those lower-level after-life realms-of-existence).

The «Unfolding Story» of how & why this came to be is revealed by the writings of the very returned (re-incarnated) Imam Al-Mahdi himself... http://www.the-testament-of-truth.com/truth/web/unfold.htm

If I understand correctly this Orion/Reptilian empire. Pretty much every planet they inhabit is either a prison planet, a military outpost, or a strictly regimented tourism business. But it sounds too that they now occupy a crest of the galaxy, not tye bulk of it.

If this is true, then there are many many prison planets in our galaxy. But we are likely the biggest one