Rather than saying science starts with observations, Popper says it starts with problems. "At this point, perhaps, we might try provisionally to define the dimensions of a problem situation. A problem is perceived as such when the progress to a goal by an obvious route is impossible and when an automatism does not provide an effective answer." W D Wall in W R Niblett "How and Why do we Learn" (1965)
Indeed, observation starts with problems. Think of what you observe driving a car, you can drive the same route for 30 years and not consciously notice specific houses or trees - it is only when there is a reason to look that you consciously notice.
Once a problem is recognised the researcher hypothesises solutions. These hypotheses can then be tested against the data, and also checked for logical consistency, cohesion with other theories etc.
It is back-to-front to put "data" first. That is an error, from a critical rationalist perspective, in traditional empiricism.
Popper rejects foundationalism. Foundationalism equates the rationality of scientific knowledge with its justification, rationality = justification = logic where 'logicality' may refer to either deductive or inductive arguments. Popper, to the contrary, equates rationality with being open to criticism: rationality = criticism = logic where 'logic' refers to only deductive arguments.