Dont rush into everything all at once.
You have lots to master in the FW
tank before you move onto other things.
Have you kept all the different species of FW
Have you been able to "maintain" this tank for a long period?
Have you been keeping with water changes over about 3 months you will be able to judge yourself on how the tank looks and are they stil alive!
Some people stay in FW
for about 20 years!
If you want SW
then i would suggest getting another tank! If you are very bored then get some more tanks to look at and care for thats what i have done!
Good luck and dont add to many fish at the same time!