I've heard mentions, but how would one go about working up an 'open world' campaign, or how have some run one? I figure a reliable home base for the players, as well as holding a session 0, but what other suggestions/ideas?

As the GM, if you're going open world you need to do a ton of extra work. This system will minimize that, but nothing can abolish it.

Firstly, are we sticking to one town or city? Maybe a planet? Whole galaxy? What's the theme? All stories need a theme, and ones set in a sandbox are no different. Red Dead Redemption is about... Redemption. GTA IV is about letting go of the past. Hell, Just Cause is about the merits of vigilantism.

Once you've got a theme (maybe a secondary one, too), start to work out the plot. You have to keep the players pointed in a direction when there are no other ideas. Don't accellerate the plot unless they do it themselves or are there for it, but keep a single far reaching goal on the table. Replace it when attained.

Start the party on this plot, but quickly spread breqdcrumbs leading to other options. For this, use of adventure supplements (official or not, even modified from other systems) and modular encounters will be great. Or, is there another plot you've got in mind but it didn't seem big enough in scope to run a game for, because that would work great.

Quickly come up with names, species, gender, two or three personality or physical quirks, and a five word motivation for NPCs and they offer missions or items or support to the party. Or they become their enemy. Or both.

Stat up only what you need.

Keep things moving at the party's speed.

It's mostly reaction and not much at all in the way of being progressive except for having a notebook of NPCs and encounters ready to go.

Take a listen to The Order 66 podcast GM Holocron episode (I believe it's episode 11). It has some great advice. One of the biggest things I took from it is Building set pieces. Basically you build a block of stats for an encounter, then you can skin it any way you'd like. Like for a bar fight, you need a couple minions groups and maybe a rival, probably with decent brawn and maybe some brawl skill ranks, then you skin that as some Aqualish thugs and the Besalisk bouncer in a cantina. Then later on down the road, you players visit a jungle world and run into some oversized primates that don't like them being in their territory, and you've already got the stats from the first set piece, two very different encounters with the same set piece.

Another thing I did with my campaign which is very sand boxish, is asked my players to come up with three goals, short, mid, and long term and to be more in depth than "get more money". Asking my players to dig into their character concept and figure out what their character really wants to do. So far I've got a corellian who wants to start a crime syndicate and a wookie who wants to ultimately free his people and a droid who wants to become the most famous/dangerous bounty hunter in the outer rim. Talk to your players, find out what their goals for their character are, and if they don't have any, help them come up with some and the direction for your game will probably become clear. And if not, have a back up plan, an over arching plot that develops in the background, that way when your pc's get stuck or are moving too quickly towards said goals you can throw them into a plot mission.

Also letting players choose their obligations and working with them to choose ones that tie well into the background storyline is really helpful, when an obligation triggers it should feel like an extension of the story rather than a complete detour from it.

Also donjon sci fi name/planet/system generator is freaking fantastic,

Makes sense, from both of you. I have the adversary cards, which help immensely, and will probably do so. And yeah, I use donjon all the time.

The biggest help I found in trying to structure and run a sandbox campaign was actually another RPG called Stars Without Number (You can find the core rulebook on Drive Thru RPG for free). The whole game is designed around a sandbox playstyle, and I stole a lot of systems, like sector and planet generation, to give me a foundation for a single sector of space that I've set my game in. Stars also has a lovely system called the "faction turn" that makes prep easy and makes the game world a living, breathing, and changing one, where you the GM stat out a few minor and major powers and have them purchase assets to attack and undermine each other, which then spills over into the actual game, and vice-versa. I've stolen it wholesale, and it makes creating flavor and context simple and efficient. What's even easier is the Stars Without Number Sector Generator online tool that instantly generates an entire sector of space complete with random names, political groups, corporations, adventure hooks, new alien species, and detailed planet and location notes! They'll take a bit of fiddling to make more Star Wars-y, but I've found it super helpful to create adventures and entire sessions off the cuff.

Beyond that resource, when it comes to running a sandbox game I find that one of the key things in my prep is character. Everyone in the galaxy has needs and wants and motivations, their own set of skills, and specific resources at their disposal, however large or small. Knowing what the NPCs want and how they'll react makes it easier to react to the players' choices and keep the game moving. What BigSpoon said about making your PCs choose a few goals is spot on! After a few sessions you'll find them setting their own adventures and impetus with limited coaxing on your part if the characters feel connected to the universe you've put them in.

The most important thing for running a sandbox game is probably a map of some description. In the case of star wars, a simple list of planets and systems the players know about and can visit will suffice (and you can always add and subtract from it). It'll allow the players to make their own decisions without constantly turning to you to provide them with places to go.

If you're going to sandbox Star Wars, I recommend having http://starwars.wikia.com/ open. It's an amazingly useful repository of potential NPCs and locations (and plots, too!).

Something that adds a lot of flavour (and ideas for missions etc...) is to have something of significance happening in the background as the players engage with your location. Perhaps the area is currently being taken over by the imperials, or there is a special festival going on, or something like a natural disaster is occurring.

Having things happen regardless of player activity (that perhaps the PCs can alter) can really make a location feel alive.

I wrote the game as we went along. We started with EotE begginer game, where Teemo the Hutt is the main villan. I spun a few details about his empire, with a path to take to bring him down. There were sevral NPCs and organizations they were involved with or brash apon, I elaborated on them further in notes, and branched sevral paths to continue.

My players followed ISOtech after working for them in Beyond the Rim, so I elabrated further about the underworld that the seeds touch and mention. My world began to grow and feel real, connected and alive.