This is not an opinion based question at all, really. Determining potential for success is a fairly objective activity. You can use math and game mechanics to determine if you're too low a level to complete something. If you want the "most efficient" level for completing something, you'll want the lowest level where success is still a likely option, again based on math and game mechanics.
The current question is objectively answerable, and not opinion based.
For clarification, a question asking for opinions would be something like "What materia is best?" or "Which character is best?" These questions are bad because they don't really require thought, and there is no single objective answer. All the materia and all the characters are generally worthwhile, and good in different circumstances. If you narrow down your question, like "Which character is best for casting offensive magic?", then it becomes a useful question again, because it can be answered objectively. Asking "Which strategy is best for this specific scenario?" is, similarly, a good question, and that's what we have here. A good answer will include sound reasoning backing up the strategy.
That said, this still isn't a terribly good question for other reasons. It could be better worded as "What is a good strategy for beating Godo's Pagoda as early as possible?" or even "What is a good strategy for beating Godo's Pagoda?" without a level restriction. This makes the question easier to approach for an answer, more generally useful, and a good answer will still give all the information requested in the original question as asked.