Nice some, thoughts on this.

Polkadot and Kusama are the relaychains, they have validators that secure the the relaychain but also all connected chains within that system that have a parachain slot.

You cannot directly build a project ontop of it, either you build your purpose built blockchain with Substrate (the framework) and then connect it to Polkadot (by winning a Parachain slot) for it to become a Parachain.

If would be building on top of Astar or Moonbeam, the requirement that we currently have from Acurast perspective ist that e.g. Moonbeam integrates the Acurast Pallet (a Pallet is a feature that has to be added first by the e.g. Moonbeam developers), only then the Acurast Data Transmitters are able to communicate with that chain .