This guide is intended to give players the most gaming experience for the least amount of money.
It is suppose to be a step by step of how to make a bare bones account. This will not address cosmetic issues.
Cartel Coins and Credits
Swtor uses both a primary and secondary currency. You have probably experienced these in other games. Here are some examples you might be familiar with; influence points and Riot points in league of legends, gold and gems in Guild Wars 2, gold and turbine points in Lord of the Rings Online, gold and nexon points in Vindictus, and countless others. Primary currency is obtain in the game through quests, selling items, dropped by npcs, or obtained through the player to player market. Secondary currency is obtained through a real money transaction (like USD, euro, ect). However, some companies include a way to obtain secondary currency in game through completing quest or what ever other actions they wish to incentivize. Turbine is commonly pointed to as a company that uses this model. There are many variations of this, one extremely clever model is the Guild Wars 2 currency exchange, in which players can sell each other secondary currency for primary currency and vice versa.
Swtor uses another variation, in which players who acquire cartel coins, a secondary currency, can purchase items, unlocks, or pets from the cartel market. They can then sell said items on the in game auction house, the GTN, for credits, secondary currency, to other players. However, there is a problem. In its current state, the players who would use said unlocks are unable to carry more than 350,000 credits and many players have not yet realized that pricing unlocks above 350,000 credits will rarely yield a buyer. That said, cosmetic items such as pets, customs, or other vanities are sure to sell for a lot of primary currency. For subscribers, who receive a monthly stipend of secondary currency of 500 Cartel Coins, this presents a source of primary currency, credits. This promotes the purchase of "gambling box"s as they could contain very rare, and thus highly coveted, items. However, those who do not wish to try their luck will most likely buy small unlocks to sell on the auction house for about 350,000 credits. Unlocks such as "Hide helm" or "addition action bar" or "unify color". So F2P accounts will most likely be able to acquire those without spending real life money.
How many Cartel Coins should I buy at a time?
The largest pack you can afford. The larger the pack you buy, the more "bonus" coins you will receive and thus more coins per dollar. Packages for Cartel Coins start at $4.99 for 450 Cartel Coins and go up to $39.99 for 5500 Cartel Coins. For your dollar you get 90.2 coins if you buy the small pack. If you choose to by the larger pack you get 137.5 coins. That adds up, quickly. You might think you are just going to make one purchase now, but as they add more and more things to their cash shop (features like addons, macros, ect) you will find yourself being "nickle and dime'd". The people who end up not getting their money's worth out of f2p models are those who think "This will be the last purchase" because so long as you are playing, there will be another purchase. Its just a matter of time. I can not stress this enough.
Should I buy account wide or for single character?
As of right now, and this may change in the future, you can only have two characters as a f2p account. There is a grace period for previous players but that will end, most likely, in December and you will have to choose which two characters you want to have. As you will probably notice, the cost of account wide unlocks is 2.1 to 2.25 times the cost of single character unlocks. This means, if you are a f2p account, you will get the most by paying separately. If they should add the ability to purchase character slots in the future, like most f2p games, you may want to, instead, invest in an account wide unlock.
What are the most important unlocks to use my Cartel Coins on?
In order to establish what is important to spend your actual money on, you need to keep in mind what you will most likely be able to buy in game. Small unlocks such as access to event gear, hide helm, a third crew skill (as preferred you have access to two which is all you need to reach 400 in a craft), and unify color will most likely be sold on the GTN as their cost in cartel coins is relatively close or below the 350,000 cap on f2p accounts. The larger purchases will be almost never sold on the GTN as they are worth more than 350,000 in game credits.
The largest, and most important unlock, would have to be the ability to wear "artifact" quality gear. This costs 1200 cartel coins per character, or just under 12 USD. This unlock does not grant access all all "artifact" quality gear, however. It gives access to pvp gear and "story" gear. It is believed that "story" refers to the level of gear that is dropped in "story mode", the lowest difficulty tier of operations. This is in line with the rest of the model, as I will explain in more detail later. As flash points begin dropping "artifact" quality gear around level 47, this is very important at 50.
The second purchase is important, however, it is also inexpensive. If you can find it for under 350,000k on your server, I suggest waiting till you can afford it through credits as it will not be as vital as the ability to wear gear. I would suggest purchasing an additional action bar for 250 cartel coins. You start out with 2 and each bar has 12 ability slots giving you a total of 24 abilities. With some hotkey'ing this is very manageable for leveling purposes. However, at 50 you might find it inadequate or inconvenient. If you have not seen it sold within your cap on your server.... those people are idiots. Subscribers already have the six bar cap. F2Pers and the only ones who could benefit from an additional action bar. So if you are charging over 350,00k for it. That's silly.
The third purchase is less important and more expensive. That would be the third crew skill. You can get your crafting skill to 400 with only one gathering skill, however, you will have difficulty crafting your better items which make the crew skill worth while without the mission crew skill. Another aspect is the gift missions. So far as I know, you can still do these as F2P. Without this type of crew skill you will have a difficult time completing your companions loyalty which unlocks bonus stats such as presence, 1% hit, critical, health, healing received, and critical damage. Those are some pretty annoying perks to be without.
What do I do when I am level 50?
There are weekly passes that allow you to do end game activities.
Weekly Pass: Warzones 240
Weekly Pass: Operations 240
These do not allow you to do ranked or hard mode or nightmare mode. If you want to do those you have to subscribe. At 240 coins a week, with the 5500 coin pack, you can buy 5.7 months of either WZ or OPS. That's 40 dollars. For almost 6 months. 86 dollar value (15/mo subscription) if you are just a pvpr or just a pver. You can access half the game for just under half the price.
Other than those, I think most things will either be unlock-able via the GTN or are cosmetic.
However, you can decide for yourself. Here are some links to help you pick what to buy.