You have already received some good feedback. You should be OK. We've been going to SXM for a long time. I would estimate that we have departed from Julianna on or almost on time about 10 times out of 30. Checked bags will definitely add some time but as already mentioned multiple flights and reduced personnel at Customs, Immigration and Security can hurt your schedule the most. We have been on flights where everyone with a connection missed it.
Having said all that, there are things in life that you can control and those you cannot. I try to balance that adage with bourbon.