It really depends on if you're optimizing for cost or speed.

If you have time constraint and need to move fast you basically pay for it with bigger upfront budgets. You will definitely "waste" more of your marketing budget going this route but you will also get you to your goal much quicker (basically, you're buying the data you need to scale).

If you don't have a large marketing budget, then you really don't have an option but to start small and expand.

In both of these scenarios it is critical to instrument your app properly so you are getting good data on conversion rates, engagement and LTV. If you're not sure that you are collecting this data properly I'd do a smaller test campaign before going all-in on a big marketing push.