Paramedical

In India, the average starting salary after a Diploma or degree in Forensic Medical Science is around INR 3–5 LPA, at the start. 
With experience, specialization, and government jobs, salary can range from INR 8–12 LPA, especially as a forensic officer, or medico-legal expert, or consultant to police or legal bodies.

Yes, Those with a Forensic Medical Science degree/diploma can apply for positions in government forensic laboratories i.e. CFSL (Central Forensic Science Laboratories) and/or similar State FSLs (Forensic Science Labs) for examples, forensic analysts, toxicologists, medico-legal assistants. 
In regard to selection, government positions are typically filled through government examinations or by way of advertisement when vacancies arise.

The biggest criterium will be biology, in order to complete a Forensic Medical Science course, particularly those that are focused on medico-legal studies.
In some Bachelor programs, a BSc Forensic Science programme may accept PCM (Physics, Chemistry, Math) students, depending on the institution. But in terms of Diploma or forensic medicine related courses, and so forth, PCB is the wisest choice.

They are two distinct career pathways. An Forensic constitutes a doctor, whereas Forensic Medical Science trains you as to where you fit in the medico-legal and investigative space. One is focused on treatment of patients, and the other is based on solving a criminal case using medical science.
If you liked medicine and law; forensic medicine (after MBBS) is a hybrid of both. However, if you are more interested in criminal investigation, using science, then forensic Science may suit you better.

If you are interested in science, crime solving, and the legal system, then Forensic Medical Science is right for you. Forensic Medical Science is a good fit for analytical thinkers who enjoy a scientific approach to biology and deduction.
You may also want to be comfortable with medical or forensic specifics like autopsies or injury reports. If that does not scare you and may excite you, then you may have find your field.

Definitely college ranking is significant, but remember ranking is not the end all be all, especially in specialised areas like Forensic Medical Science. 
What is more crucial is the institution's exposure to the profession, laboratory facilities, and rapport with industry partners. 
Having attended a lesser-known college with forensic programs and good placement assistance is better than attending a top ranked college with less specialisation in forensic science. 

Yes, many colleges may admit students for UG Forensic Medical Science based on Class 12 results in any human Science (science stream). You can see on their websites what there admission to Diploma or undergraduate courses on forensic medical Science will be without the need for an entrance exam. 

That said, there may be some reputable universities (or postgraduate programme) that may require you to take an internal exam or interview, so please carefully look at the eligibility when considering application to the institute.