Is X ship playable in the game?

As a general rule of thumb, if the ship was a warship in active service with any of the 7 major powers during WW2, it is almost certainly in the game. The only consistent exception being that in Song of Sirens, the smallest warships that players need deal with are destroyers. Ships such as corvettes and destroyer escorts were not included for feasibility reasons. If, however, a ship you want to play is not in the base game, feel free to add it! Players should work with their GM to add their own ships to a campaign. 

X from the setting of SOS makes me uncomfortable. Why was it included?

Song of Sirens was written to be a historical fantasy system initially set in 1930. As it has a basis in our world in 1930, it is not a great place. We understand that there are a lot of things that would be common in the setting that might make players uncomfortable, and we acknowledge that. Since the system is a semi-historical setting, we felt it would be disrespectful to brush over some of the worst parts of history, so it was included in the game. If, however, any of those elements in the setting make you unable to enjoy it, feel free to change it in your personal games. Also, as the setting can get really dark in certain places, it is recommended that GMs have a discussion on what players are comfortable with them having in their campaign. 

Can I play as an Admiral of a nation that isn't one of the seven major powers?

Of course! When setting up your own game, you can play as whatever nation or faction that you want. Song of Sirens is built with the intention of the player being from one of the big seven, but other places, especially Spain, China, Turkey, Brazil, Argentina, Chile, and The Netherlands would all be quite viable choices. It will be more difficult, and some things may need to be tweaked, but if you're okay with needing to put in some extra effort, you can play as any nation of your choice. 

Do Sirens have to be female? Do Admirals have to be male?

No! Male, female, neither, both, it's all well within the bounds of the game. In fact, we encourage you to be as diverse as possible with Sirens and Admirals. While Sirens will usually take on the characteristics from each nation's general culture, you can research less well known folklore, mythology, and culture to craft a unique character that perfectly fits how you like to play.