Hindi taught the fast way for a Bengali native: by contrast, not from zero. Same word order, same postpositional structure, large shared vocabulary. The lessons spend their words on the small set of things Bengali doesn't have — gender, the ergative ने, and the schwa-deletion habit — and skip the parts you already know.
Part I · The script and sound
Devanagari is the same abugida system as Bengali script, so most of it transfers. What's left is a small set of new letter-shapes, five Persian-origin sounds, and one rule (schwa deletion) that fixes most accent.
Part II · The structural skeleton
The core grammar — pronouns, postpositions, case, gender, and the ergative. Twenty-five words and four rules carry most of the structural load of any Hindi sentence.
Part III · Patterns in the wild
The vocabulary of actual usage — Bollywood lyrics — by frequency, with the coverage curve that tells you exactly how much to learn for how much understanding.