Is there much of a difference for a non-electing church plan to go with a 401k vs 403b? Does using a 401(k) make it subject to ERISA?

Also, as a TPA, I'm having a tough time seeing what role we would have in adminstering a church plan. If the document has to be individually designed and maintained (which we do not do) and there are no 5500s, discrimination testing, etc. for us to provide service on, then what, if anything, is there for TPAs to do?