After the adoption of the resolution, the board shall cause to be prepared any necessary plans and specifications of the project, and estimates of the repayment obligations of the district, together with an assessment of the amount of the cost, or portion thereof as determined by the board, apportioned to the various tracts of land in the district according to the benefits that will accrue to each such tract by reason of the expenditures of the money for the project, or for the repayment obligations of a contract.