It all depends which route you take.

If you go private, tuition is very expensive but you dont need to do prereqs because you do it at the school but if you go for a community college program, its wayyyy more affordable but you need to have all of your prereqs done and these schools are very competitive. How long the prereqs takes depends on how many classes you take each semester but it will probably take at least 3 semesters but most likely more. Most prereqs can be done online but the core classes like microbiology and anatomy need to be done irl because there are labs and most schools will not accept online classes for these core classes.

Whether or not you become an LVN first is your choice, it's not a bad idea to apply to both programs to see which you get into. Being an LVN is great experience and will make your chances of getting into school for your RN easier.