To begin with, you are unlikely to rank for shorter terms - so you have to go with long-tail.
Produce content for each stage & collection of terms per stage. This not only increases the number of terms you are likely to rank for, but naturally means lower competition.
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Over time, your site gains "weight", and it is easier to rank for shorter terms.
But you still produce content for each stage, and you still target longer queries.
Just be mindful of "term value".
Longtail may be "easier", but typically has small audiences.