I have a lot of years doing what you are looking to do, I am aware my account was also created today so I have no history here so, I guess my advice is of the same value as the other new guy offering help BUT!
My advice:
1. don't take this client
2. if you must take this client, who is liable for the actions? This industry has huge risks, I have worked with huge budgets, they have literally 0 times ever been sent to me in total first, check your own legal structure, are you a sole trader? Do you have a LTD company to hide behind or indeed fold if it goes wrong? (it will go wrong)
3. if you are totally bulletproof legally, go ahead, if you manage to get anywhere near ROI, msg me, and I'll hire you straight away (dear moderator, I am joking)
Seriously though, don't take this client but do take the experience of trying to work out how to address it.