yoga class descriptions

Want to join boxing, suggestions/help?
The issue here is that I’m a 5 foot 2, 17 year old girl that weighs roughly 125 lbs., in addition to being a vegetarian- and not the most nutritionally-conscious sometimes.
I have really strong leg/thigh muscles, almost no upper body strength. Fun stuff.
I wasn’t going to start anything too difficult, maybe start with a class at the Y or something, but I know I’m not in the shape required to get into this full-out. Still, I want to get something out of this.
My question is:
1.) what would you suggest to someone fitting my description? Are there other classes I should begin with first [I've had yoga shoved at me a few times and considered it]?
2.)Do I need to make any changes before going in to start a class or should I just wait and go with the flow?
3.)What should I expect from this? How much strain will it be, am I making it out to be more than it is or I in for an even bigger surprise? x3
Haha thanks ahead of time.
Anastasi, i like the ideal of your going to do boxing, but after i read the rest of your short but sweet bio… it came to mind that in my opinion, again just my opinion… you should be in kick boxing ( strong legs ) you mentioned your strong points and as a mma amateur fighter and boxing coach im always teaching to stick with your strong suits ( it feels natural) and develop your weak ones to become a complete fighter. you can do it for fitness or you can do it to really learn to defend yourself ,over all you sound like a smart person and thats half the battle to becoming a fighter.
Raga Shivranjani Description