Think hard before introducing a free plan. People invest their time in your product, so may (i) introduce a support burden, and (ii) be unhappy if you decide to start charging. It's not an easy two-way door.

People who submit their credit card are serious about trying your product. This is partly through selection bias (only those who are serious will sign up) but the act of entering a credit card also encourages people to be more serious about trying out a product. (This could be because they want to feel consistent: I entered my credit card, so I must be considering this product seriously. I'm considering it seriously so I can't just not bother to log in during the free trial.)

I'd go for 2 to start with. It is likely to maximise trial->paid conversion, whilst reducing # trials. This will be easier for you to manage (in terms of support costs and customer discovery), and it keeps the door open for the other options later.