Understanding Credits: Explorer vs. Pro Plans for New Users

Hello, I have a question about credits that I imagine must come up often for new users: I am evaluating the product so I plan to sign up for the monthly subscription to start. If things go well, I'm fine to commit to annual. I am trying to decide between Explorer and Pro plans. I have a list of several thousand (between 3k and 7k) contacts that I want to run enrichment on and there are at least a few new fields I need. Because of the way the waterfall works, the number of credits I need seems to be non deterministic, right? So, if I start out on the Explorer plan and blow through my credits in one go, can I upgrade to Pro without being penalized? In terms of credits, the Pro plan seems to offer a lower price point per credit.