I was wondering if it is fine to write
From this project, I have learned [blah blah], and this is the most important harvest I have received from this project.
What is a better metaphor or better way to express the meaning?
The most important benefit I have received from this project is having learnt that
would avoid needless repetition and still convey the intended meaning.
I would say this is the most important thing I have gleaned from this project.
Glean has one definition of "To gather (something) slowly and carefully in small pieces." It also has a relationship to harvesting, with its other definition: "To gather (grain) left behind by reapers."
This is the greatest reward I've reaped from this project.
How about finding?
This is the most important [or significant] finding from this project.
NOAD lists, under finding:
a conclusion reached as a result of an inquiry, investigation, or trial: experimental findings.