If you ever had the opportunity to look under the covers on a project like this, you would find that all the complexity is manufactured.
It's not even the 80/20 rule. It's more like 99/1 rule. As in, I see this requirements list, and I have two options for you. A) I can deliver 99% of what you want for 1% of your stated budget, or B) I can take 1000% of your budget and still fail to deliver 100%.
The sooner you abandon any software design and engineering principles such as estimation and planning you will find that your project will start seeing more bugs and will be developed far more slowly.
It's not even the 80/20 rule. It's more like 99/1 rule. As in, I see this requirements list, and I have two options for you. A) I can deliver 99% of what you want for 1% of your stated budget, or B) I can take 1000% of your budget and still fail to deliver 100%.