In my view, there isn't a stock answer to your question. Since your client is engaging a 3(16) fiduciary, they have a fiduciary duty to assess the potential risk of loss/costs to the plan that could result from the proposed 3(16) fiduciary's acts (or omissions). Without seeing the scope of the limitation of liability/indemnification provision or the scope of services they will provide under the agreement, not sure how one would quantify the limitation. I mean the agreement must be reviewed to determine what is the possibility of, and the maximum amount of, any potential loss for the plan based on the services provided and, perhaps, if these potential losses were to arise, what could be the additional administrative or other costs for any actions your client may have to take to mitigate/minimize the potential losses? (Editorializing here but honestly, many agreements that purport to be 3(16) agreements don't even provide the third-party being retained enough discretion to, and/or require any services that would, cause them to be fiduciaries).
That said, the bulk of our clients are plan sponsors. We frankly invariably strike all this limitation language and advise our client to tell the proposed providers that they should ensure they have good enough E&O insurance to cover their negligence (and indemnity to us) and that they must provide the client with documentation indicating that they have an ERISA 412 bond that covers them separately with regard to their fiduciary acts involving the client's specific plan or one that covers theirs and the client's actions under the plan both but separately (i.e., with separate $ limits). Our clients generally stick with this and don't sign providers who will not "step up" if they are at fault.
On the other hand, when we advise clients that are TPAs regarding limitations/indemnities, the form contract generally includes 1-year fee limits. These TPAs, though, generally charge much higher service fees (basis points type fees) than what your proposed provider is charging. Also, as with most indemnity provisions, this amount is almost always the subject of heavy negotiations and does not remain static... the agreed upon limits range from elimination of the limit to a multi-year limit to sticking with the original 1-year fee limit (here, the ultimate limitation depends on the scope of the work and the fees generated under the contract... how much do they want the business).