1. What advice do you have for those with very little IT experience looking to get started in this field?
A person cannot expect to walk into a place of business, loudly declare "I want a job in IT!" and expect to be given a job. Learn a language - literally any language - and it will be a skill people will pay you for. I recommend SQL - it is simple to learn, free /online, and a way to build a knowledge base on what you're doing.
2. For entry-level roles, how much do experience requirements on job postings really matter? Do candidates have to meet all qualifications / requirements in a job posting?
Two things in the qualifications section matter: what degree, and how many years of experience. Even things that seem mandatory, Finra Licenses for example, aren't 100% necessary unless expressly written. Language is often vague on purpose to avoid lawsuits through plausible deniability, but degree and minimum years experience can be legally rigid requirements.
3. Given the tendency for some orgs to turn job posting "requirements" into wish lists, how can a prospective employee determine if they're truly qualified?
Some orgs have lengthy requirements sections in their job descriptions on purpose. I may or may not have written "Prior knowledge of Muffler Ball Bearings" into the requirements section of a bank's job description. Whatever.... Yes, I did it. Nobody said anything. Digress: the overly-lengthy requirements sections are meant to scare you away. Read the first 4-5 bullets and if you fit, toss 'em a rez.