Finetune an existing Google Sheets Document plus develop a dashboard

I have created a document in Google Sheets that is made up of multiple worksheets. I need this to be further developed by someone with a higher capaability than what i have. The following needs to be acheived: [1] to Understand the existing formulaes used and if there are better alternatives then to rewrite these. The aim here is to ensure robustness of the calculations and to improve any processing speed. [2] The design currently allows for a budget to be created for a fixed 12-month period. We need to change this to a rolling 12-month period [3] To be able to add additional input lines by selecting an 'Add Line' icon. Currently we have to insert a line and then re-write formulaes to allow for the additional lines added. [4] Monthly P&L data is currently pasted into the document every month from Xero (accounting programme). We need to be able to do this less manually. If you are unfamiliar with Xero, it is a relatively easy programme to allow for this type of feature. I believe there are many apps available to facilitate this. [5] Need to develop a dashboard to improve the read out of the data. Dashboard to be developed in Google dashboards and ideally this would be displayed in another php built programme/website. In order to correctly understand this project we will need to talk it through. I am only interested is Freelancers who are already familiar and have expertise with Google Sheets and DataStudio. Preferably also have experience with capturing information directly from Xero. I have written numerous notes in the document explaining requirements. To add to this: Would also like to add some forecasting features that are not currently built into the worksheet.