Upon release, Star Citizen will have two major components: Squadron 42 and the Persistent Universe. Squadron 42 is the single-player campaign for the game that allows you to work your way up to gaining citizenship and preparing you for the world. The other aspect is the Persistent Universe, the MMO portion of the game. The PU allows players to explore, interact, mine, fight, and whatever else they want to do in space. Check out the official trailer for a general idea.
The official response is no. Even though ships can be purchased to help fund the development of the game right now, ship sales will stop closer to the game's release and will instead only be attainable by purchasing them in-game. Additionally, CIG is really trying to make this game about player skill rather than based on stats, therefore a player may own a powerful ship but not necessarily know how to fly it particularly well. Players will still be able to purchase UEC when the game launches, though this is more to counter "gold farmers" and there will be a maximum amount that can be purchased.
Can't decide between the Mustang and the Aurora? It is ultimately a matter of what you think you'll want to do as a star citizen. The Aurora is roomier and built more for transport, whereas the Mustang is speedier and meant more for racing. Both can be viable in combat depending on your flying skill and how you outfit it. If you find you're unhappy with either ship, you do have the option to upgrade to another ship as well!
An expanded list of all ships in Star Citizen can be found here. Otherwise, you are currently able to fly the following ships in Star Citizen: 300I, 315P, 325A, 350R, Aurora CL, Aurora ES, Aurora LN, Aurora LX, Aurora MR, Avenger Stalker, Avenger Warlock, Avenger Titan, Constellation Andromeda, Cutlass Black, F7C Hornet, F7C-S Hornet Ghost, F7C-R Hornet Tracker, F7C-M Super Hornet, Freelancer, Gladiator, Gladius, Khartu-Al, M50 Interceptor, MPUV Cargo, MPUV Personnel, Mustang Alpha, Mustang Beta, Mustang Delta, Mustang Gamma, Mustang Omega, P-52 Merlin, Reliant Kore, Sabre, Starfarer, Starfarer Gemini, Vanguard Warden.
UEC is the in-game currency for Star Citizen. It is what players will earn in order to purchase in-game goods and services. Purchases made with UEC are permanent and will carry over into the Persistent Universe. You are able to purchase it now for actual real life money if you want to, but it is not recommended as you won't really be able to spend it on much, and all the things you could want to spend it on can be purchased with REC.
REC is the currency used specifically for Arena Commander and Star Marine. Players earn REC by playing in PvP and Co-Op modes, and use them to rent ships, weapons, and equipment for use in the AC and SM modules. Purchases made with REC are not permanent, and will not carry over into the Persistent Universe. When you use REC to rent something, you have that ship or item for seven 24-hour periods. When you log in after making a rental, the first 24-hour period begins. If you decide to take a break and log back in a month later, the second 24-hour period will begin.
While there is no release date for Star Citizen currently, project lead Chris Roberts states there will not be a traditional commercial launch, but instead when the beta is deemed "good enough", they will declare a formal release. However, the game is playable as it is developed, like many modern titles. Roberts also states they recently entered the "content stage" of development, where the underlying technology is mostly complete, and world building and gameplay can be focused on.
This is only just occurring because a lot of new technology had to be developed to execute the game to the scale and fidelity the game aims to offer. The latest released roadmap takes the development to the end of 2017, around which time the game can be expected to enter beta. It may be reasonable to expect initial launch (which will not include every single feature listed in the RSI stretchgoals page and countless other outlets, and will make about 60 of the 110 planned star systems available) by the end of 2018.
Special thank you to NJDFisher for this writeup.
The first taste of what life in the Star Citizen persistent universe will be like. The current persistent universe module is the testing ground for what will ultimately be the MMO aspect of the game. Players can explore and communicate with one another in various ports, access their hangars, and get in their ships to fly around space. Though the amount of things you can do still may feel limited, this is a big step toward the endgoal and should be seen simply as an early representation of the incredible things to come.
If you have any ships that are currently hangar-ready, you are able to load them into your hangar and see them in all their glory! You can see it from the outside. You can climb inside. You can admire it. You can sit in the cockpit and make laser sounds with your mouth just as you did when you were a child dreaming of being in space.
To access the Arena Commander module, load the game and hop into the Simpod in your hangar to enjoy PvP space combat, PvE space combat, limited space exploration, and racing. Keep in mind that not all ships are available in AC just yet. A list of all the AC-ready ships can be found in the FAQ above. During "fly free" events, you will also be able to fly ships you do not own to help with the testing process.
Coming soon-ish, the first-person shooter module will be released.
Luckily, there are some really great resources out there if you just can't seem to find all the information you need from the Star Citizen website.
It should go without saying that the official Star Citizen forums have a plethora of information for players ranging from newborn to veteran.
The Star Citizen subreddit has a vast amount of collective knowledge to find the answer to just about any question you have. Be sure to read the FAQ there before asking anything, however, or they will kill you.
The team at the Imperial News Network does a great job each week of supplying transcripts and TL;DRs for the latest Star Citizen videos, in addition to providing their own fan-generated content.