Split by stage when each stage is its own search with its own intent and SERP, and let one page span the funnel only when the query and results support a single journey. The deciding question is not how much you want to cover but whether the stages are actually distinct searches. One page can orient and convert at once when people approach the topic as a single connected path and the results reward a comprehensive guide. The moment each stage shows up as a separate query that pulls a different kind of result, you are looking at distinct searches that each deserve their own page.
A single page spans the funnel well when the query reads as one continuous journey. The searcher wants to understand the thing and decide about it in the same sitting, the SERP is full of thorough guides that do both, and the stages blur into one reading session. In that case a guide that orients, compares, and points to the decision serves the whole arc on one URL, and breaking it apart would scatter authority and force the reader to hop between pages for a need they experience as continuous.
You split by stage when the stages are genuinely different searches. If the learning query and the buying query are typed differently, mean different things, and return different result types, one page cannot satisfy both without diluting itself. Trying to span them produces a page that is too broad for the decision-ready searcher and too transactional for the learner, so it serves neither well. Distinct intents with distinct SERPs are the signal to give each its own page tuned to its own stage. The pivot is single-journey-query versus distinct-stage-searches, and the SERP shows you which one you have.
Before you split or combine, check whether the stages are distinct searches. Look at how people phrase each stage, what each query seems to want, and whether the results for each are the same kind of page or different kinds. If the SERP supports one journey, build one comprehensive page. If each stage is its own search with its own intent and results, split and tune each page to its stage. Read the searches first, then decide the structure.