Well, you can persue it while still being wary. Look out for red flags as you proceed.
It seems like they aren't sure what they want yet, so open a dialogue with them and look for signs of evasiveness.
Let them know how expensive it will be to commission and purchase the copyrights to this large order. If they just vanish, or try and give you excuses or guilt you into charging less, pull out. Ask them questions about who they are, the project and their needs. If they are forthcoming and it all sounds legit, discuss the terms of the job, draw up a contract and have them sign it. If they won't sign a legally binding agreement, pull out. Be sure to include a portion of the money to be paid before work begins, and make sure this payment clears before proceeding. Don't compromise on a deal where your rights will be given up.
Since they do not have an exact number (about 30 or so is not precise) I would suggest a per-chibi price, remember they said they want to purchase the rights, so you need to do a higher price than you would for personal use.
Then if they go ahead, you need 1/2 up front, and the remainder prior to delivery.
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Anyone else gotten notes from this account?
Proceed (with caution) or avoid? And if proceeding, any suggestions on what to ask?