You don't need to tell your wife that you're seeking your own legal counsel. There's a reason they put that littel "v" between the names of the parties in these situations -- it is, by design, an adversarial (and confidential) system.
If she finds out, simply say "I decided that it was wise that I run whatever mediation agreement we end up with, past my own attorney before signing it" -- nothing more. Or maybe a "I decided that it would be wise to better understand my rights and responsibilities here; this is new territory for me, and certainly not anywhere I planned on being." Or something similar.
Considering what you're saying about your disparate financial capabilities, yes you need to protect yourself against your wife dragging this out. I've certaily seen it happen. But you don't need to let her threat of that stop you from getting some basic initial legal counsel, so you can start better understanding what your rights, responsibilities and potential vunlnerabilities are here.
