Designing the "user experience" for labs without giving too much away
As @MassimoOrtolano mentioned in a comment (and I think this extends to all lab courses, not just EE), "the main factor is the time constraint." Clearly your suggestion to make the preparatory/emphasized steps "cookie cutter" and the learning objectives more open-ended is a way to approach this time constraint with balance.

It sounds like your main concern is in determining which of these steps should be cookie cutter and which should not. You give two approaches: start from the beginning and work forwards, or start from the end and work backwards.

However, that assumes you are going into this with no information. That might be a principled approach in some cases, but if I can be a Bayesian for a moment, you are missing a crucial piece of prior information: you should have some idea of what your learning objectives are before you even start.

The approach I would take is to first identify learning goals, then sketch out the procedure and identify which steps are relevant to the learning goals and which are not. Cookie cutter those that aren't, leave open-ended those that are. Surely, this won't produce a perfect lab course on first pass, and it might take some tweaking over time, but it seems like you expect this and it is a better approach than either extreme.

Second, involve your students in your goals. I think it's best to think of students as if they are quite capable and smart. Let them know: "I designed these labs so that I give you a step-by-step through some of the things that aren't relevant to the learning goals of the day. At the start of each lab, I will provide you with a list of the intended learning goals. I am looking for feedback if you either a) feel like you are spending too much time on something that isn't a learning goal, or b) feel like the answers are being handed to you for the things that are."

When in doubt, it seems like it makes some sense to bias towards cookie-cutter towards the beginning of the course and towards more freedom in the end, but that depends on how well the different pieces fit together and how complex the problems get by the end.