Can we watch transactions / UTXOs?

Possibly? Needs more investigation.

  • Watch transactions / confirmed blocks API https://github.com/input-output-hk/plutus/blob/master/plutus-pab/src/Cardano/ChainIndex/API.hs

  • Watch utxo adress for all known outputs, watch address until given slot https://playground.plutus.iohkdev.io/tutorial/haddock/plutus-contract/html/Language-Plutus-Contract-Effects-UtxoAt.html