Understanding Lead Lists and Token Usage in Clay Trial

Quick question, I am currently experimenting with really small lead lists in clay to understand the functions of the stuff. I am still using trial and have 2 thousand tokens available. If I use them completely and ever think of upgrading my plan (which I will) do I have to pay for them? Also, when there is some leftover credits after trial and I upgrade my plan, do I take them over to my paid plan? Cheers