The sortition process isn't quite like centrally listing everyone and picking from the list. The Verifiable Random Function (VRF) allows you to know "I was picked!" and create a short quickly verifiable certificate to prove that to someone else. Is a distributed fashion all the nodes run their own check to see if it's their turn to propose or verify and then take network actions based on that.
Algorand allows more than one node to propose a block to make sure that >=1 nodes propose a block with high reliability. The distributed consensus process picks one block to be the block.
The number of validators is more like 30-50 but that's a global tunable depending on what kind of system properties you want. Fewer can be faster and more can be more secure, but there's diminishing returns and 30-50 is so far secure-enough and quite fast (5 second round times on the current global network).
Algorand allows more than one node to propose a block to make sure that >=1 nodes propose a block with high reliability. The distributed consensus process picks one block to be the block.
The number of validators is more like 30-50 but that's a global tunable depending on what kind of system properties you want. Fewer can be faster and more can be more secure, but there's diminishing returns and 30-50 is so far secure-enough and quite fast (5 second round times on the current global network).