What should one prepare for when starting yoga? Am I going to be sore all over the next day? Should I get a mat? How often would you do it?
I really do want to try it out.
You will need a mat for sure, and as to soreness, that depends on a lot of things: how fit and flexible you are, how often you work and stretch the muscles that are used in the yoga practice you choose, and the level of yoga you practice. If you choose a more strenuous yoga like Vinyassa Flow you may be sore the following day -- especially your shoulders from holding downward dog. Yoga is very individual: you get out of it what you put into it. You're pretty fit so you could choose a challenging class. You may not be able to achieve third tier poses (I've been practicing yoga for years and simply lack the confidence and balance needed to stand on my head), but they're not necessary for a successful workout.
Before I got sick I did a sun salutation of about 15-20 minutes every morning, and an hour long class 1 to 2 times a week.