I can't believe no one's done a wide-guide yet. There're plenty of wide players on higher difficulties around here, even a couple of us peaceful-wide players.
I'm working on a peaceful Piety guide right now for Deity difficulty, but may do a Liberty semi-wide tall guide at a later date.
On higher difficulties, you can aspire to play wide peacefully, but it won't always work, depending on the map and who your neighbors are. If you're the kind of player who doesn't feel comfortable adjusting your strategy 30-50 turns into the game, then it's probably best to start with a Liberty CB rush of your neighbor. That guarantees you enough room to go wide even on standard Deity, regardless of civ. I think there's a CB rush guide floating around, so just use that one for the start. Remember, it's 100% okay to build a settler as Liberty before you get your free one, but don't do it just to have another city, only do it if settling early will block off the AI expansion and give you at least +1 additional city spots in the future.
The key is managing happiness and growth, as in, making sure certain cities do NOT grow in the early/mid game and making sure certain cities DO grow. As a general rule, after the first 50 turns, I plot out exactly where I want my 6-10 cities to be, exactly how much happiness I reasonably have access to, and their exact max populations before Ideologies. I then make sure to switch my cities away from growth and into heavy production/gold once they hit their limit. To distribute your population, divide your cities up into what their purpose is. In a peaceful game, I always make sure I have 3 high population cities: Science (with mountain and NC), Culture (with all guides and Hermitage), and Trading (coastal, with some farmland, some tile gold, good resource diversity, and East India Company). For a military game, I would scrap population growth on either the Culture or the Gold one, and put it toward a Production city instead (with Ironworks, and forest/hills). The remaining cities, I would designate as science cities (anything with mountains) or gold cities (everything else) and divide their populations based on my victory condition (SV and CV focus on science; Diplo/Domination focus on gold).
Settle your new cities one by one to avoid transition happiness issues (so, build a road to the city while settler is in production, settle the city, then immediately use workers to connect luxury; repeat). You should start with your empire limits and chokepoints to prevent AI expansion into your zone of control, and then fill out the areas with unique luxuries within your zone of control (have 1 mercantile city state by this point), and finally fill out city spots that are useful but do not have unique luxuries (have two mercantile city states by this point, and another city state ally if there is one with a unique resource you don't have; this step also requires zoos unless you are going down Patronage left side).
If you are playing on Deity or Immortal, this should set you significantly behind, and you should not expect to be at tech Parity until the Modern Era (although, with Great Engineers, you can still snipe wonders starting in the Renaissance Era with beelines; and Louvre/Big Ben/Porcelain Tower are generally available pretty late). This means you should rely more on international trade routes and less on internal routes in the early/mid game (at no point should more than half of your routes be internal routes; Liberty starts are gold-needy and science-needy).
Generally, Commerce/Exploration work well as intermittent trees to get between Liberty and Rationalism (or as replacements for Rationalism for Domination). Patronage for Diplo. CV can go many ways.
