That woudl be perfect
Both fish are compatiable with each other
Yep, CUC would be vital too. Go for 10 critters eg a Cleaner shrimp, 4 hermit crabs and 6 various types of snails to cover all types of algae etc
Good, 25% water change a week is great
If you choose to go with corals, you dont need to add any liquids for calcium etc as your water changes shall boost them up.
You also dont need a protein skimmer for that size tank. For my 12 UK gal, i dont. I run an Interpet PF3 (fr 3ft tank) with all media in it(phosphate remover etc) and a powerhead. I keep 2 clown fish and a cardinal along with coral, CUc and an anemone..... touch wood i havent had any probs yet, except for a pH drop which killed my cleaner shrimp as i lowered my powerhead, thus cutting down on surface aggitation.
I run an air-driven protei skimmer on my seahorse tank though as i was experiencing some oily surface scum and ill be feeding twice a day
Dont worry, marines not difficult at all! Good luck