While there are many publishing software programs available, unless you have design experience, it is best to get a professional to assist you. It will give you a better result, less frustration and save you time and money. This is a complicated question. If it fits into your plan, budget and customer profile, yes. If it doesn't, no.
Advertising can be expensive.
Question 4 lists lots of other options. Choose the most efficient way to reach your customer at a price you can afford. Little or no marketing will surely cost you sales. Marketing is not a sure thing, some things work and some don't. Look at several options.