This is a huge topic that could go forever…but first things first…prior to buying equipment you need to decide some things. I think knowing the questions to ask can help guide you
1) Which type of salt water fish aquarium do you want?
-Fish only aquariums – Only fish with no other marine life.
-Invertebrate only aquariums – Only invertebrate creatures with no fish.
-Invertebrate and fish aquariums – A combo of the first two.
-Coral reef aquarium –amazing to look at if a bit trickier to maintain.
-Specialty aquarium – focuses on just one species.
2) Where should I put my saltwater fish aquarium tank? You have it set up but if you are changing over I am sure you get you should do this once otherwise have a crane handy. Think space, cleaning/maintenance,flooring, aesthetics, practicality.
3) Your 38gal will work well although tanks below 55 gallons need more maintenance and care
4) What fish to start with in my saltwater fish aquarium? Beware of mixing aggressive and gentle fish. You’ll find the gentle ones go belly up!
5) Consider using wild vs. raised fish for your aquarium.
I hope this helps but until the basics are decided its just not possible to give equipment ideas.