Reply-first, post second is the honest order for the first few months.
The reason is mechanical. A post from an account with no history has no distribution behind it. The feed has nothing to test it against, so it goes to a handful of people and dies, and you learn nothing because the sample is too small to read. A reply borrows distribution. You are inside a thread that already has an audience, and if your reply is the most useful one there, the profile visit is the conversion. At zero followers that is the only channel that works.
What makes a reply land is specificity, not volume. Reply to accounts roughly in the 5k to 50k range in your niche, on posts that are still moving in the first hour, and add the thing the post did not say: a number from your own account, the exception to their rule, the step they skipped. "Great post" is invisible. Five of those a day beats fifty one-liners, and it builds the list of people who recognise your name before you ever publish.
Then make the profile do the work. If someone clicks through they need one line that says what you post about and one example that proves it. Pin your best post. That is the landing page, and most small accounts leave it blank.
On posting, pick a format you can repeat rather than a topic you find interesting. A fixed shape, a teardown, a before and after, a weekly number, is what turns a stranger into a follower, because the feed gets something to predict. Three posts a day in a different style each time gives it nothing.
Premium is not a growth hack, but early on it buys a few real things: longer posts, editing, analytics you can actually read, and replies appearing above non-Premium ones in some threads. If you are reply-first, that last one is the only argument that matters. Take it for a month and compare reply impressions before and after rather than trusting anyone's claim about it.
One number beats follower count for the first few months: profile visits per thousand impressions. Followers are a lagging signal from a decision someone already made on your profile, so fix the profile first.