Do I need bitcoins (or any other currency) running in a blockchain?

Yes.

The blockchain itself is just like a database, is perhaps the worst database of all .

However, a database does not "rotate" an application. Typically the opposite, an application consumes it. This is exactly what happens with most coins, such as Bitcoin, mentioned by you.

Bitcoin only records transactions, these transactions need to be "accepted" by miners. They are responsible, through a work test, for including your transaction in the blockchain. At every transaction fees must be paid.

The amount of fees depends on the size of the transaction. Transactions include various information, the inputs (the unspent transactions), the outputs (the recipient), and the signature (the cryptographic signature). The more information you have, the more expensive it will be.

One way to store arbitrary content in blockchain is by using OP_RETURN , in Bitcoin it's limited is by 60 bytes. There are coins that have no limits or higher limits, or other specific features.

Each coin has its cost and confirmation time, this should also be considered. At this same point, each coin has its own blockchain. You will have to have the respective currency, if you use the Dash blockchain, you must have Dash (not Bitcoin) . You should also look for "strong" coins, after all any blockchain is vulnerable to a 51% attack and if the coin is "discontinued", your data will be lost.

Other currencies, such as Ethereum, allow you to run an application using DApp. But, anyway, it's not free either. You will have to pay Gas for it to "run".

You do not necessarily need to insert everything into blockchain, doing so would create multiple transactions and spending multiple currencies. You can enter only one hash, originating from a hash-tree . Thus, you will be able to check the integrity of multiple data with just one hash.