You can use Float's Spreadsheet Input tool to easily copy and paste your forecast from elsewhere into Float. You can also use this to copy budgets from one scenario to another. While you can't upload directly from a spreadsheet, you can certainly copy your budgets right in.
You can also use Spreadsheet Input to move easily between cells and enter your budgets more quickly. And you can click and drag a cell to the right to copy it forward.
Spreadsheet Input is currently available in the 'Base' scenario but not on scenario layers