So I know the basic premise of Touhou - the independent shooter games. But I'm a little confused as to how so much depth has been added to characters, and if it's mostly due to fans. How does one get into Touhou?

Basically, are there any sites/summaries that can help out a Touhou beginner? I feel like I'm missing out on a big portion of the reader given how many Touhou doujins there are. I'm a little overwhelmed by the sheer amount of content/characters.

Personally, I just started reading the doujins and the stuff in the Canon tag, and eventually got to know the characters that way (although I still haven't got a grasp on the one with the headphones and their crew). I'd never be able to get through any of the games, and LPs of it don't tend to show endings so not too much use there.

There's always the Touhou Wiki: http://touhou.wikia.com/wiki/Touhou_Wiki

The fastest way to get an overall grasp of what's going on would be to read Perfect Memento in Strict Sense and Symposium of Post-mysticism

Also, LPs, transcripts, and whatnot. The wiki has everything except the endings, but the endings are generally semi-related comedic bits that don't matter much

i quote above,
i had the same problem few years ago, and it seemed impossible cause the quantity of fanworks, because the fanworks are more usefull to understand that world,
anyway, the original manga Silent sinner in blue is a good start,

i begin to read touhou djs like they were original one-shot, and slowly i started to recognise the characters,
you better not worry, because, for example, characters among the most loved, like Alice, are depicted is a lot of different manners,
play the games is an help, but is usefull only the first encounter with new characters, infact i think very few people can see the true ending,

As a former fan of TH, I quitted on the coming out of TH14, due to getting tired of keeping up w/ the ever-coming new characters.