Hi Lisa
To do this I think you are going to need a ‘join’ table - say called Client Tasks - which would enable you to check off a particular task for a client in the way you want.
If I understand, the issue you have is that of creating these task records - it may be possible to automate this. I did some work for a client of mine automatically creating records in a similar way. This involved using Zapier to build some processing logic (with Javascript within the ‘Zap’) - so the new client would cause the Zap to create the new task records automatically.
You should be aware that this requires a paid Zapier subscription and that ‘Zaps’ don’t run immediately - they are either every 5 or 15 minutes depending upon the subscription.
If you’d like to discuss this with me further, please get in touch (bear in mind time wise that I am in the UK).
Julian