Freelance tax questions

I've been doing freelance programming work for the last year, and have completely neglected to do anything about my taxes. Yes, I realize this is probably pretty stupid, but here I am.

That being said, I've lived very frugally, and have saved ~75% of what I've made. My expenses have been minimal, and I've kept records of all my purchases.

This will be the first year I haven't had a job which takes care of my taxes for me. Previously, I've just used TurboTax for them. Honestly, I find the US tax system to be very confusing, and I was just looking for some answers to some basic questions.

1. Would TurboTax still be acceptable to use?

2. I'm planning on writing off 80% of the rent for my home office (not the whole apartment) and internet connection. Any other write offs I may be forgetting?

3. I'm married, and my wife has a regular job. I'm not sure if this changes anything with our joint filing. To be honest, I haven't formed an LLC, sole proprietorship, have a business license or any of them (this part does worry me a bit).

Happily, I live in a state that has no income tax. So I'm assuming I won't have to worry about any state taxes.

I just feel really uncomfortable doing this without the typical employee provided W-2 and the like. Any advice and guides/resources would be very helpful. I've done a good amount of web searches, and there seems to be a lot of conflicting advice.

And lastly, is it really terrible that I've waited this long? I know I can file quarterly, but as I said, I've saved the majority of what I've made so far, so I wouldn't have a problem writing one big check to uncle Sam.

Thanks for reading, and I look forward to any answers and advice you all may have.