Yea, it's pronounced INN-uss. It's an old family surname and one of my favourite names. I personally would prefer to use it on a boy, but I can see it on a girl too. I just wouldn't want people to mistakenly think it's pronounced ee-nez, like the Latin name - sorry to anyone named Ines out there, you have a lovely name, it's just not what I'm going for.
Innes is an incredibly noble, classic sounding (and looking) name to me. I'm having a hard time thinking of middle names that would flow well with it though.