M.A Hindi

You may be eligible to apply for M.A. In Hindi.

Hi,
I am here to solve your problem. This is the complete solution for your query. Check out:
https://www.shiksha.com/college/dakshina-bharat-hindi-prachar-sabha-thyagaraya-nagar-chennai-19798/admission

Since you don't have any Bachelor's background in Hindi it's hard to say. I would suggest IGNOU as it's relatively easy to get. But, it could be difficult to get admission in government colleges. But, enquire with individual colleges who have MA Hindi.

You need a Bachelor's degree to be eligible for any Masters course, regardless of subject.

Yes, you can. For Masters from any subject, you must have graduation.

After completing graduation, you can apply for masters in Hindi

Kuch mahatvapurn kitaaben-
1. Hindi sahitya ka itihaas (ramchandra shukl)
2. Hindi sahitya ka saral itihaas (vishwanaath tripathi)
3. Hindi sahitya ka itihaas ( dr. Nagendra dwara sampaadit)
4. Hindi bhasha evam saahitya ka vastunishth itihaas (saraswati pandey, govind pandey)
If you want to read more, then read all the books of important critics if you have. Names of some critics such as Hazari Prasad Dwivedi, Bachchan Singh, MS Suman Raje etc. The above four books will help you a lot for JNU, M.A. Hindi entrance.

Some universities might allow you but it is hard to say. If there's an entrance then you could just prove your caliber in the same and easily secure admission.

Yes, you can join MA in Hindi, you are eligible for this.
Good luck