Is Sand Okay for a Seahorse Tank / Aquarium?

Sand is very much okay. A thin layer of live sand, preferably black, is the ideal substrate for a SHOWLR (Seahorse Only With Live Rock) tank, which is type of seahorse setup I prefer.

Should I Get A Protein Skimmer?

Yes, please. Although seahorses can certainly be kept successfully without the use of a protein skimmer, I recommend including a good skimmer for best results.