Where did the Hyperspace Routes in the Star Wars universe originate from in the first place, Also is there only one route on and off a planet? Or can a world have multiple Hyperspace routes?
In Legends canon, hyperspace routes were discovered by the Hyperspace Navigator's Guild:
Hyperspace Navigator's Guild This ancient guild was responsible for the discovery, cataloging, and availability of hyperspace routes. Founded originally on the planet Empress Teta, the guild was made up of daring explorers who braved the unknowns of deep space to find quicker ways to get from one major trade center to another. Once a new route was discovered, the right to use the route was sold by the guild, with a percentage of the royalties going to pay the explorers who found it. The guild existed without major change for many millennia until New Order (sic), when the Empire raided the guild's computers and made off with whatever information it wanted.
(Source: The Complete Star Wars Encyclopedia (2008), Vol II (H-O), page 71, entry "Hyperspace Navigator's Guild")
The Essential Atlas shows some planets located along a single trade route, while others are located at the nexus of several, such as Coruscant Corellia, and Brentaal. It also elaborates on how known routes are maintained:
Updating and recalculating well-known routes is the duty of the Space Ministry. Updates are available for a nominal fee from ministry offices or downloaded as a standard part of docking procedures at many spaceports. As part of the same process, route and sensor data from starships' navicomputers is routinely uploaded and collected for analysis by the ministry's astrogation bureau, after which it becomes part of new updates. Refusal to share navicomputer about established routes is illegal, and almost universally condemned by spacers as selfish and dangerous. That doesn't apply to data about new routes, however: Scouts, smuglers, and legitimate captains all guard such knowledge jealously. Put any group of spacers in a cantina and within a couple of rounds they'll be telling fanciful tales of spacer guilds, shipping companies, and entire species that supposedly make their living from secret trade routes.
(Source: The Essential Atlas (2009), page 14)