Which Provider should I use?

I am a beginner in Ethereum. I want to build Application to write data which can be read by any of the users. The app must be robust, scalable, secure. So, according to my studies, I prefer Ethereum rather than Hyperledger (I am still open for the suggestion). Now there are a couple of questions:

1. Should I deploy it to public blockchain or make the private blockchain.

2.  Will public blockchain cost real ether for 1 particular transaction.

3. Infura is the provider that is used to deploy into the public blockchain. Are there any other providers in the market or Infura is best.

4. If I want to deploy private blockchain, what should I prefer? I read something about Kaleido but I don’t think it is good enough.