Hi Irene, and welcome.
We have found mosquitos to be a problem in times with no wind, so I guess it would depend on the weather conditions while you're there.
Serafinas is still in Marigot, in the marina on the side opposite Tropicana. Its near a great restaurant called Cool "something". Maybe someone here could help with the name. Serafinas is much smaller than it used to be. I would not feel safe to go to the marina at night and I have read others on this forum that feel the same way.
I have always felt safe on the French side. That is where we always stay. Of course, common sense will tell you to not wear flashy jewelry anywhere on the island, and to follow safety guidelines as you would anywhere...
Have you considered staying on the French side? Grand Case Beach Club (GCBC) is a wonderful gated place and you can walk into town for dinner if you wish.
Best of luck with your trip, and congratulations on your marriage!
And, of course, we all expect a long trip report when you get back!