Do i need to get lessons on bass guitar to be a pro?

and how long does it take to be really good?

If you know nothing about guitar is wouldn't hurt, to be a pro takes time and a lot of talent, guitar is not a thing that you learn overnight, you have to put in a lot of practice time and lots of hard work, those strings on a bass are not easy to play, they are very thick, you need good callouses. To be a pro you would have to work on a daily bases, and if you have the talent and are a quick learner maybe three years. I know when I was first learning I use to set my alarm for three or four in the morning so that I could get in practice time before work, then I would practice two hours later, and then another two at night, most people are not willing to put that much time into study. Some people have perfect pitch and seem to learn a lot quicker than others but this is rare, some of your musical geniuses can learn to play well in three years, but this is also rare. Most rock players that bang did not learn their instrument in a couple of years, they have been playing since they were kids. Everything depends on how ambitious you are and how much time your willing to put into studying.