My primary aim is to get as much publicity as I can get.
Thanks in advance
I think you should have a basic free offering but also a premium paid offering right from the start.
It's really challenging to charge people once they are used to getting something for free. It's also not a good business strategy because what people use for free they might not pay for.
Develop a Minimum Viable Product (MVP), have 2-3 tiers of pricing (with one being free) and go from there. That model has been successful for a lot of SaaS companies and there is no customer confusion about wanting to charge for your product.
Turning a free service into a paid one is of course legit but will give you a very bad publicity. It would be much better to either have a premium version from the beginning or somehow (specially if you want to turn into a paid service very soon after launch) keep it free for the users that signed up at the beginning (in the end, they are doing free beta testing for you)
I would say yes, and definitely yes.
Or, you can let the early adopters use the site for a while (6 months?) after you convert. Remind them monthly that their special treatment will end on a certain date, so they are not surprised.
Also, how much does it cost you to let them use your service. Often it is zero. If so, why not let them keep using it for free?
It's also a good idea to have a free option MVS (Minimum Viable Service), regardless of how many people use the service before you start charging.
Don't overestimate how many users you will have, even if you give it away for free. You may be surprised at how difficult is to get people to use your service, even if it is free. (I am speaking from first-hand experience.)
I suspect that given the small number of users and low cost it will make sense to keep them free. Once you are big, rich, and successful, you can tell them they have to pay. Until then, having more users will generate momentum.
Another idea is to ask a favor of them. "We are converting to a paid service. Since you have been an early adopter, we are going to allow you to continue using the service for free. Could you do me a favor? Can you give me feedback about how we can improve? What made you decide to start using the service in the first place?"
Take a look at Seth Levine 's breakdown of pricing models. I found it to be very helpful when thinking of my own pricing model. For your situation I think you should consider: