Creating Project Structure

Dear All ,
This is not purely technical question but also require some
project management Skill. Please let me confess that i am newbie in using ganttchart .

So my problem statement is as follows. I work as Tax Auditor and i have to perform auditing , demand and recovery of Federal Tax.

I have made a excel control chart to monitor the work which has 10 sheets where each sheet is one of my work activity . I am reproducing one of them .

Now each row is a dedicated to client.

Similarly each sheet will have some similar information and start and end date .

Now if i have to use a project management tool how should i go about organizing them .

Shall i define each of my activity corresponding to one of my function as a project with each of the assesse or client as one activity with start date and end date.

So i will have 10 project and each time one client comes i add it as an activity .

Is there a better way available . I am also giving the link to the control chart in excel for better clarity .
https://www.dropbox.com/s/bmmifs6su3snbzu/CONTROL%20CHART%20-%20Copy.xlsx?dl=0