I can't quite figure out what you're supposed to do there. It's starting to look like sort of a sandbox, but without all the amazing economy and industry and player markets etc that defines good sandboxes. i.e. Eve. Since you can bypass the entire thing by literally buying ships with real life dollaridoos, the in-game economy will sort of become meaningless, I fear, and thus the sandbox will too.
Heyo! So two main things here with the cash purchasing of game and then the 'sandbox' Player Universe stuff:
$$ Cash $$
The fancy/expensive ships they sell for cash during development are generally 'limited time' sales, as in they are only ever for sale one time, in limited number, and then you can't buy them again for real cash after the sale is over. So some of the big capital ships or the super fancy luxury yachts or whatever that all these whales are buying, you only had a few weeks to buy them before you have to earn them in-game. Imagine a limited edition Eve Titan that you could just buy with cash, or eventually in game earn with ISK (some of the pricier ones you can not earn in game, ever). Some of these ships are also limited in number in-universe, so whatever capital ship yard won't produce another one for sale if there is already a certain number owned by players.
I'm not sure if they ever changed it but it was my understanding back when I followed this constantly that all (except for the starter ships) direct ship sales will stop forever once the game launches Star Citizen game bucks for real bucks
Basically PLEX, you pay real cash and get space credits for your character. This was a big kurfluffle a while back as you can imagine the pay to win implications, I believe the current thinking is they will limit the amount and frequency of what you can buy so you can't just load up and splurge on a titan or whatever, more useful for ship weapons and smaller vessels. But I'm sure they'll see those dollars and rethink it. Remember Star Citizen does NOT have a subscription fee, basically buying SQ42 single player gets you lifetime multiplayer access.
They had some interesting points on this basically saying a lot of older players are not interesting in grinding it out for days to be able to get a slightly larger ship and are happy to spend some money on it.
We should back up just a second though that in this game the larger ships are not always 'better' but more like, different tiers of gameplay and commitment. A difference from EVE would be that in this game you absolutely cannot solo operate a Titan. So even if you -could- get a hold of one by paying cash, the ships needs a player crew to be remotely effective using it, and a dedicated org worth of resources and protection to keep it operating and safe. There's no log-off for the larger ships, they are persistent, so you won't be solo-farming in your supercapitals in Star Citizen. There is however a sweet spot where some ships really just are flat out better for a bit more money and might not need many other people to kick your butt with it. But in general the bigger the ship the more of a headache they are going to be to operate by yourself without spending a bunch on half-assed NPC crews and other resources. Stargates and transit is size-dependent in SC, so larger ships aren't always the best way to get from A to B or the fastest. I think the idea they are going for is you can do most of the same things in a lot of the different tiered ships, but it's way more fun with your friends in the larger ones if that's what you wanna do.
Economy
This will be pretty reactive to players but they are scaling player influence depending on 1.0-0.0. IE if you are mining asteroids in Jita you aren't going to be able to corner the market, and the NPCs are doing most of the big orders in those areas. Out in scary neighborhoods players will make up much more of the manufacturing, mining, and mission creation. You'll also of course make more money hauling goods out to further areas, and generate content for escort type missions and 'raid' missions for both players and NPCs. They are going to have thousands of NPCs running through the economy along the players hauling, mining, selling, attacking, etc, -supposedly- adjusting to what's going on and to keep it interesting for you the player.
All of this is of course a bunch of talk until I really see it working, but the 'theory' is that Space Trucker (player or NPC) agrees to a haul order for 1,000 Veldspar in 0.0 or whatever and wants to haul their goods to sell. They might put out a mission for an escort or crew for the trip. Opportunities for other players or NPCs to work crew on the ship or to escort the hauler through bad neighborhoods. NPC or Players who are into being bad might get a 'tip' on paying for information that a cargo is coming through their area and be able to try and intercept. On with the dynamic content. They will also have lots of 'missions' with more narrative focus ala the quests you might get in WOW or something, with chances for people pro and anti to be a part of the semi-randomized mission tree.
The idea is to pair you up with people you'd want to play and interact with. You'll have a 'slider' and be able to set some odds for % encounters depending on your pvp or skill level. Note that the slider will never be able to be off all the way, and it is useless in the 0.0 type of areas. If you are a carebear that just wants to haul, you are still going to get ambushed in highsec, but you probably aren't going to run into killer death squad pvpers very often. But if you go to null you still get trounced.
Player economic activities include player owned territory on planet surfaces for farming, drug manufacturing, prospecting, mining, running a shop, manufacturing, etc. In space there's hauling, personnel transport, escorting, patrols, defending assets, the usual space pew pew options. In the more lawless areas you can find abandoned starbases to claim, although you have to work with tons of people to get all of the things fixes and operational, and all the usual null bloc activities. It's a pretty good range (SUPPOSEDLY LETS SEE IT IN ACTION).
Wanted to add a quick not on travel and system sizes, they are aiming for it being kind of a pain in the ass to cross multiple systems, some of these are like 30 minutes wide at 'warp' and require multiple stops for refueling along the way. So hauling across several systems or traveling across the galaxy is actually a very long trip that will take most people a few days of play time.
https://robertsspaceindustries.com/starmap if you want to see the current starmap. They are aiming for content-rich systems that you can do plenty of things for a long time without needing to leave. Aiming, of course, we'll see