Filecoin and IPFS interactions

The following things are separate but related in the following way:

• The IPFS codebase
• The Filecoin codebase e.g. (Lotus)[https://lotus.filecoin.io/docs/set-up/install/] <- assumes a Filecoin-configured IPFS node is running locally (code / “all Filecoin nodes are IPFS nodes under the hood”)
  • That code seems to be where lotus interacts with ipfs, which it does. It adapts between its blockstore accessor and ipfs assuming there’s a local ipfs node running. I guess that local ipfs node will be configured to connect to the Filecoin-IPFS DHT and not the public IPFS DHT
• The IPFS network <- a standalone network for storage but with no incentive structure for persistence (you just make data you’ve got locally available on IPFS by publishing it, others can download it, but if you go offline, that data isn’t accessible any more)
  • This network is specified/seeded by a bootstrap list
• The Filecoin network <- separate networks (“Filecoin nodes don’t join or participate in the public IPFS DHT”, “Filecoin is the missing incentive layer for IPFS and verifies that your data is being stored, while maintaining the efficiency, authenticity and resiliency provided by IPFS”)
  • In fact it looks like the filecoin network is an IPFS network (separate to the public IPFS DHT, let's call this the Filecoin-IPFS network) and separately a Filecoin blockchain network?

OPEN QUESTION - does Lotus run IPFS in-process? The Lotus install docs don't specify needing to separately install an IPFS node, but the code looks like it's assuming an IPFS server is (can be) running locally.

OPEN QUESTION - is the filecoin network two layered networks (IPFS + blockchain on top) or is it all one libp2p mesh?

OPEN QUESTION - when specifying, say, a list of CIDs for a Bacalhau job to run on, would we expect to be able to specify CIDs in the IPFS network, or the Filecoin network? In the latter case, they would be sealed, and need to be unsealed. Assuming we specify the CIDs as IPLD addresses, can IPLD reference files in the Filecoin network?

OPEN QUESTION - how can we play with a Filecoin network without spending actual FIL? Can one set up a dev instance of Filecoin to play with?