some good advice being bandied about here. i think you will find that in photography there is no single formula for success as each successful photographer will have a unique story as to the path they took.
my own path started with assisting (something i highly recommend) which led to second shooting which led to main shooting. i have been working solely in the field of photography for over 10 years now and it has only been in the last 2 years that my business has started to transition into me taking a more leading role rather than providing support for other photographers. patience will be an enormously important attribute.
there will be no comprehensive answer to the question you posed (too much stuff to cover not enough time) but i'll contribute a few thoughts.
this is where a big part of the patience comes in but where an great deal of knowledge can be gained that you wont find online or in books. assisting multiple established photographers will give you an opportunity to learn several things including different techniques with different gear, different philosophical approaches in terms of style, and maybe most importantly different business practices. if you are successful at assisting it will also offer you something that i have found invaluable...a network of working professionals that can provide you with back up for gear and shooters as well as access to jobs when they can't shoot something or don't want to shoot something. i still assist for others to gain access to new types of shooting and to maintain those relationships so that when they refer a job they can't do they call me first. this has been the number one most important thing that has fueled my success transitioning into a main shooter.
the pitfall here is that you have to be completely supportive of whoever you are assisting and NEVER promote yourself under any circumstance. i have seen countless people try to assist but were too eager to be the Man and it showed on other peoples jobs. they faded fast and lost access to that professional network that could have kept them afloat. additionally, i have seen many people try to forgo assisting in favor of running their own business immediately and ultimately they fade away as well (typically in under a year) because they are under prepared and arent aware of the numerous mistakes you can make that will ruin a business faster than you can say bankrupt.
i approach this with the mind of an assistant (complete support of the main shooter) but it provides the environment to safely refine your craft as you dont have that direct pressure of having to deliver for a paying client on deadline. 2nd shooting has taught me how to see light better, how to introduce light appropriately into available light, and the full capabilities of my lenses and cameras in a variety of situations. after a couple of years your decision making/problem solving becomes lighting quick. an important asset if you want to be a main shooter.
this one is tricky for me as i have never in my 10+ years advertised myself....not even on facebook. every opportunity i have had has come through word of mouth. that is not to say i dont think advertising isnt important, i am gearing up to do my first run of advertising this off season.
i guess my feeling on this can be summed up by the question What and Who are you advertising? if you are just starting out then it is more than likely that you dont truly know who you are as a photographer and don't really know what kind of photography you are capable of providing in a professional manner. you may say that you want to do family portraits but when you actually get out there and do it you might discover you arent that good at it. if you advertise for that and it turns out not to be your strength then the word-of-mouth machine will work against you pretty quickly.
again, with a little patience, you can take some time to develop your techniques and style, do jobs in a safe environment, develop a portfolio that is professional that showcases work that YOU KNOW you can deliver competently and THEN advertise who you are and what you do.
there are thousands of other considerations that go into starting a successful business but i will end on this thought. be careful what you wish for. lol. running your own business (successfully) typically means you need to be available 7 days a week at 12+ hours a day....if things go well. running your own business can also mean lengthy dry spells, whether that means not having work for a few weeks to a month or doing jobs that clients are on a 30 to 60 day payment schedule (or worse 90+). because of this unpredictability, i have found it beneficial to remain diversified. i currently assist 4-6 photographers regularly, teach at a university, 2nd shoot for 3 different photographers, and shoot for myself (Weddings, Corporate/Collegiate Events, Architecture/Real estate, and Studio/Location Portraiture). i have in the past also worked at a lab, taught at a 2nd College, been a studio manager, and handled post production for several photographers.
all that being said....i have a really cool freaking job and i feel blessed that i get to do what i do. if you feel that you have this same passion then you will be fine and figure out your own path for success.