For initiating, you have to find out what works for you and your partner. Some like to be surprised suddenly, some like to cuddle and let it lead to it, some just ask. My boyfriend and I simply ask each other "Wanna do stuff?" when we are in the mood and that is our cue, as silly as it sounds. But that is what works for us. It is worth asking her what she would prefer as she may either be unpleasantly surprised or not get the cue or be turned off by any method.

To be more passionate, again, is up to how you feel and what works. Just don't hold back, let her know for example how beautiful her body is, how seeing her nude makes you feel, what you want to do to her, how you've been thinking about this for so long, how much you've missed it, how good she smells/tastes/feels etc. Just say what is on your mind! When in the act, hold her close tightly against you, wrap your arms around her, kiss her all over and look into her eyes. Don't be afraid to just act on it if you feel the need to hug/kiss/take a break to tell her romantic things.

As for being rough, this should definitely be talked about to avoid crossing boundaries. I wouldn't worry about the size difference. But ask her how exactly she would like you to be rough. There's a huge difference between 'getting a little rough with playful spanking' and 'trapping her arms together behind her back and forcefully gripping a fistful of hair'. Pain tolerances as well as emotional tolerances vary from person to person. Some may call it quits at a slightly reddened handprint on their behind, while some can get very, very extreme. I would not go much further than simply upping the intensity of what you already do until you ask her what she would like to try.