2. Compute and store checksum for each files. It should be much faster than asking Bitcoin Core to perform reindex if you also worry about file corruption/integrity.
Can you elaborate on this please? Computing and storing checksums will certainly help with integrity, but how will they help in speed?
I mean computing checksum/hash than using one of Bitcoin Core features (such as verifychain[1] or reindex).
[1]
https://bitcoincore.org/en/doc/29.0.0/rpc/blockchain/verifychain/Bitcoin Core v30 will only make this worse, which is why the logical conclusion is that Bitcoin Core v30 is a de-facto attack on the network and Knots 29 is the only thing we've got to corner spammers into irrelevance (and not to mention the whole CSAM-on-the-blockchain attack vector as well)
As reminder,
1. OP_RETURN doesn't enter UTXO set/chainstate.
2. It's possible to add malicious arbitrary data on Bitcoin blockchain with other approach and it already happened long time ago.