There are a large number of ...

There are a large number of considerations to this. Firstly there is establishing the demand from the  subsequent uses and what period the reservoir will need to support to size the reservoir.

Then there is the question of abstraction from the stream and legal permissions to do this and is the rates and volume sufficient to supply the demand? Any effects on downstream users and natural habitats?

How will the abstraction be done, designing a suitable pumping system. Conrolling the abstraction pumping?

What is the quality of the stream water  and since it is a stream how will it vary with flow and seasonally? What treatment and disinfection is required for the unspecified uses. What can be done with treatment wastes?

How the whole scheme can be financed in capital terns and what operational and maintenance costs will there be to support it and is there the technical base locally to support and maintain your proposed solution.

There will be many others but this is a selection of the principal challenges as they occurred to me.