Looking at the galaxy map, there are a few routes between say Alderan and Coruscant. Do you actually have to make several jumps to get there? Or, do you just use them to get an idea of the travel time and/or difficulty and go from 1 place to another in 1 jump?

In reality (so to speak) I'd say you'd have to stop for major course changes, like when changing from one hyperlane to another. Other than that you could do the jump in one go if you wanted to. When playing, however, you need to make as many jumps as the GM feel suits the story.

When my players do long-distance travel like that I pretty much hand-wave it unless the outcome of the dice roll is important somehow. I tend to call for Astrogation checks only when it matters, like when evading pursuit, racing someone (or time) to get somewhere, and so on.

Yeah, narrative-wise is doesn't matter if the PCs have to roll 4 times or just once for astrogation. Unless the journey IS meant to be the adventure - for example in the Maw, or densely packed area of the Galaxy (the very core). I always assume (influence of the X-Wing/TIE Fighter games) that there are mid-stops, which can be used for short encounters (a ship asking for help, a mysterious container etc.) but are usually ignored mechanically wise, since I want the players to get to their destination.

I usually use the mid-stops only when there are 'unspent' threat/boon symbols on the astrogation roll.

I don use hyperspace routes. If you want to go from A to B then you just go fom A to B.

The only time I have them roll astrogation is when under stress, unusual conditions, difficult routes, or they want to save time. How long it takes is rather abstract, and depends on where they are going. Hours to a few days if staying in a sector, days to weeks if traveling to different sectors, and weeks to months if they want to travel further.

Nice thing about hyperspace in the Star Wars universe is there is a logical reason for hyperspace travel to go at the speed of plot; stellar conditions varying can have a big impact on travel time. Depending on the stability/straightness of the local hyperlanes, it's often faster to not go in a direct line between destinations. If a bunch of asteroids happened to drift across the usual route and slow the trip to dodge them, or that recent supernova removed a gravity well that blocked travel over a different path, you can speed things up or slow them down easily. Though in general more travelled routes are usually faster, that's why they're more travelled after all (and more people = more astrogation data = easier to calculate faster routes). But of course if you're trying to go someplace in a STEALTHY manner, a different approach might be needed than the usual routes...