If you qualify for Jersey Care you can't get marketplace insurance, they will just tell you to contact Jersey Care
When applying for the Marketplace you are estimating what you will make for the calendar year. If your estimate is higher than the amount JC eligibility you will be eligible for the Marketplace and potentially a subsidy as well. At the end of the year they were reconcile and you may end up with even a higher subsidy if your income is lower then estimated.
In short if you would like the Marketplace, estimate high. You probably won't get audited but to do it correctly have a reason why you estimated high (expected a bonus, return in an investment, started a side gig etc)