I'll start with reading speed. I know that for me, speed can be affected by my level of focus, distraction, and the complexity of the material I'm reading. For instance, Reading a short story by Raymond Carver, with his sparse language breezes by. However, switching to Dickens, with embellished, and sometime run-on sentences, I find myself re-reading passages just to get what's going on. There's also differences for me between reading for pleasure (novels, etc.) or reading more technical materials. I think you can get a ROUGH average, but understand that words or pages per minute may vary widely.
As to an approach, I find that the best way to change a habit is to just put the taks I want to do on a to-do list. Rather than a goal of 12 books, think of it more from the perspective of reading EVERY DAY. Don't get nuts about 12 books. If you only read 10 or 11, great. If you make it up to 15, great. Repitition is really the only way to start or change habits. Making it a regular thing to set aside some time every day to read...whatever you're comformtable with...15 minutes, a half hour, an hour...and just READING in that time is more important on the habit side of things. When changing habits, I tend to avoid setting SPECIFIC goals. For instance, if I'm picking up a book every day for a half hour, but at the end of week 2, I'm only halfway through, I'd tend to get frustrated and think "Why bother?" If I decide to go to the gym regularly, I'm going to avoid looking at a scale because I don't want to think, "This is useless! I'm not losing weight as fast as I want!" Once I've established the HABIT, that's when I start setting specific goals WITHIN that habit...and that's what I'd recommend.
The most important thing is to set aside the time, put it in a calendar or on a to-do list if that works for you, and just make sure that you do it every day. Soon it will be as natural as eating lunch, you'll have an idea of how quickly you devour books, and can figure out how to challenge yourself within that habit.