Humm, so bitcoin.conf is like one autoexec.bat, in this case i should install bitcoind and then i just need to use bitcoin-cli and thats all?
Yes.
Using BITCOIND RPC require interacting with the Blockchain, and therefor downloading entire Blockchain is required before starting accepting Bitcoin Payments.
Or I am wrong ?
And the goal of OP from what I read, is to use RPC API in order to interact with the blockchain without the need to download it completely.
In this case, he is looking for a free API to handle that for him, so blockchain.com is good for that, you can also check coinpayments to accept more than 60+ cryptocurrencies.