Q: Do I need a protein skimmer with this?
In a 10g, you really could go either way. I would because it will keep the frequency of water changes down, and the skimmer will keep the water quality high, allowing for a decent bio load.
Q: Do I need a filter or could I go with a powerhead?
If you go with a skimmer, I'd go with the Prizm skimmer by Red Sea Aquatics, around $70 US. Very easy to set up, and works well. No other circulation of filtration would be necessary.
Q: What exact fish do you guys suggest for me as a beginner to marine?
Two of the hardiest fish, nice and active, would make for good beginner fish are the stripped (banggai) cardinal and the ocellaris (false percula) clown.