My thoughts, in the order I thought about them
3)
I use an enrolled agent to do my personal and LLC taxes. The cost, around here, is much lower than a CPA. An enrolled agent is just as, or more so, versed on tax codes as a CPA. The CPA is also licensed to audit the books of a public company; something your LLC is not.
1)
I'm a little fuzzy on the rest, but this is roughly how we filed last year. Talk to someone that's up on things.
You can contribute 20% (I think) of your LLCs profits to a SEP IRA. This is in addition to any personal contributions you make to a 401k and a Roth. The SEP contribution will directly lower your tax burden. My wife and I are both on the LLC so it was split between a SEP for each of us. Note, this is the employer side only. You, as the employee side, may not be able to contribute to the SEP IRA at all. Down the road, you will be able to roll a 401k (when you leave your employer) or any other rollover IRAs to the SEP if you want to consolidate.
We maxed out 401k, couldn't contribute to Roths, and pulled 20% of the LLC money into SEPs.
2)
As I understand it, if you met or exceeded your tax liability from 2006 (should be ok if you have a regular job with regular withholdings), then you shouldn't pay a penalty if you wait to pay taxes. Increasing withholdings from your paycheck for the next few months may help with that.
4)
For the amount of money you're talking about, I think an LLC might just be easier overall. One of the benefits if you incorporate is that you can retain money in the company and then take it out as you need. Or, you can draw a 'reasonable salary' and then take the rest of the money as a dividend (never felt comfortable with this personally, but I know many that do this)