It seems like some local fishermen tend to offer some of the lunkers (LMB) they catch to new pond owners as a good gesture. I could see this happening in my case as well. I assume this is not a good idea for a brand new pond (5 acres), even though it could be introducing some good genetics. If I am correct at what point is it ok to accept some of these big boys. I don't want to offend anyone by not accepting their thoughtful gift, but I also don't want to screw up my ponds food chain.

Don't accept the fish.
Your mission is to create an environment conducive to long term success. That means you build a food chain, first. Then, stock the appropriate numbers and sizes of predator fish, based on your stocking plan. By stocking a few large bass early, you'll lose control over the initial stocking numbers, increasing your odds of failure, long term.

You figure a 5 pound bass is going to be 18"-20" in length or so. That means it would prefer to be eating BG in the 5"-6" range. Not too many brand new ponds have large numbers of BG in that size range to feed 1 let alone several bass of that size.

Also, there have been studies done showing the survival rates of larger bass transferred to a new body of water is often low. You can use that as an excuse to kindly turn down the bass offered to you...

I had the offer of an 8 pound bass about two years after my pond was stocked. I turned it down; but sure thought about it a few times wondering if I did the right thing. FWIW: I still think I did.

You'd be pretty p*ssed if you introduced some kind of parasite or desease.

I have some pure Florida LMB certified genetics recently stocked in 1/4 acre brood pond for transfer to main pond for my son - he's a bass fanatic.
I'll soon have to start removing to prevent overcrowding - hate to throw them on the bank!

See if Todd or Bob want them for resale.

A brand new pond isn't good for any kind of fish. As Bob said, your big bass won't find any fish to eat. Smaller fish won't find anything either. I think that it's smart idea to leave such pond without any fish for some time to create a natural wildlife in it (I mean all kinds of insects, small creatures and so on).
There won't be any plants in the beginning too - fish usually don't enjoy such beach-like ponds.

Disagree - add forage fish as soon as there is enough water

If only you are planning to feed them (somehow I dislike all that fish food and I prefer fish to be fed in a natural way).

Forage fish will find things to eat. It's amazing whats in water and we don't even know it! All kinds of little microscopic animals to munch on! Plus day after day more stuff will begin to emerge in the water. I don't think you would have to feed them anything if you didn't want to.

I added the LMB, BG, and CC to my new pond within a month of it being dug (late summer after a freak storm that filled it up 2 weeks after being dug) and got a pond full of nice fish. Lots of invertebrates to eat but no feeding by me. This is the recommendation of the DNR to help keep undesirable fish out.