Free vs Charging

The more users you have the more difficult it is to change (the product, pricing, etc.) without a big blow back. If you plan a free product and set a price later on, I would advise to go with "time-limited offer", "special launch discount", ... in order to set expectations.

At my 16-year-old SaaS business, we've been through multiple iterations of pricing. My suggestions:

• create the product for the high end of your chosen market segment
• and charge them, more than feels initially comfortable. You want to start with the folks who have the most pain (i.e. willing to pay more).
• you can create lower-priced offerings over time once you identify the major use cases and market segments where your product resonates. Don't cannibalize your high-price clients unless competition forces you to.
• BUT: it's even better if you can start pricing high and then identify more valuable use cases/customer segments and enhance the product over time. This lets you raise prices.
• freemium can get you users, but in general their feedback is less useful for product direction. Also, free users tend to require more support. Upgrade % tends to be very low, and will likely approach 0 in the limit. I would only consider freemium as part of a marketing campaign to raise awareness in the target (non-free) demographic. Be sure to plan for real $ and time spent supporting free. It may end up being more cost-effective to spend that time and money on other customer acquisition strategies.

Best suggestion is build for a niche where people need a solution and charge them for it out of the gate.

I think you should only make a product free if you plan to monetize it via ads/affiliate links/etc., i.e. not by charging the users. You can add optional paid features though. But I don't recommend changing the product from free to paid overnight, better give discounts to the first users like @smirolo suggested. You can also say the the product is free forever for those who joined before the paid plan, but it does not make a lot of sense, in my opinion.