Thanks for your extensive response. It answered my question. However a new quesiton arose. What is the maximum size of data which could be stored in the tangle with one single transaction? Since there are no fees I could theoretically store a mass of data without paying anything. If I got it right, it is just enough to confirm two other transaction to attach my transaction to the tangle.
There will be a size limit for Tangle. IOTA will use automatically local snapshotting to handle it. The full Tangle data can be stored in permanodes for long term storage. The Permanodes are like a storage marketplace on top of IOTA. But you have to pay for it. In this case, tangle is more like a transit real time data storage place like what happens in this use case -
https://www.coindesk.com/trust-odometer-blockchain-test-aims-turn-tide-car-tampering/To know more about snapshotting and Permanodes -
https://blog.iota.org/iota-development-roadmap-74741f37ed01