I'd wait another few weeks before chopping, but also consider not going so low yet (the nursery lady may have had a point), not trying for an instant bonsai, but maybe going to a foot now, giving a few more potential options to work with and you can always cut again another time.

To prevent suckering, you need to put down something strong, not just wood chips. You can start with the strongest cardboard you can find, covered in chips. Once it pushes through, cut the shoot and reapply cardboard, raking temporarily the chips aside. This will not eliminate but reduce suckering, and weaken the tree faster. I have some stumps cut in 2009, many injected with fungi to accelerate decay and get something edible, and they are still suckering now. If you want to minimize work, put down wood planks. Those should be enough to prevent suckering for 3 years, probably resulting in death of the stump.

trees heal themselves .... NEVER fix them.. until they are broken ... yours isnt broken ... i think jean missed the beetles reference: LET IT BE ... LET IT BE .... SINGING WORDS OF WISDOM.. LET IT BE .... ETC ... ken

Let me make sure I've got this straight. Did they cut into the trunk or just give it a hurricane cut? if they cut into the trunk its dead. If they just gave the branches a severe trimming it should be fine. But if that's the case i wonder if they just replaced the old ones with new ones. Many places still give palms a hurricane cut for transplant. I personally prefer to keep a full head of leaves for transplant. Even if some leaves die back this fine because the palm will gain nutrients from the dying leaves.