awgh, cool, thank you for the insight. I wasn't aware of this. There has been a specific visa for this purpose for decades, but it is good to know that the short-term work permit can also be had on top of a visa-exempt entry
No, it's not advisable to have multiple travel insurances for one trip. Most policies will not pay out if you have overlapping coverage. It's better to choose one comprehensive policy that meets all your needs
It's not illegal to be dual insured, but it can make claiming more complicated. For example, if you needed medical care abroad and had two travel insurance policies that could payout for the claim, you won't get double the money. Instead, the insurers would decide how they will split the bill . . . .