Do you need all transactions in this new book? Or just like monthly entries? How transaction-heavy is this client? There's a tool that will help you populate additional books, but last time I used it, it wasn't spectacular. Also I'm not fully sure it will work from secondary book to secondary book. I only recall using it from primary>secondary.
Also just an FYI that the more you have of amortization, FAM, Rev Rec, & high activity, the more complex it's going to be if you're using the data population tool and just in general.
I'd definitely recommend getting an expert involved and of course testing in Sandbox first. Agree with above that a certification may or may not mean anything, but it would be good to get someone involved who can prove they've dealt with it multiple times.
You can create all sorts of problems for yourself if you mess it up.
Source: started doing multibook when I didn't fully know what I was doing. Created all sorts of headaches for myself and in some cases others. Luckily nearly all in Sandbox.....