I've done this before. I own my business and have for 5.5 years. I also counsel business clients and set up LLC's and Corps as part of my job.
An LLC is great for liability protection, but talk with a CPA about filing an S-Corp election. This will allow you to take a reasonable salary (upon which you pay employment taxes as an employer of about 15%), then anything over that reasonable salary does NOT incur the employer taxes. So you save 15%. It's huge in the long run.
I generally recommend that you use that savings to beef up your retirement. You can use a SEP IRA or a Simple IRA (depending on whether you have employees or not). You don't need a 401k for a small business - the fees are way too high. I have two employees and have a simple IRA. Works great and is cheap.
Talk with the CPA about setting up Quickbooks. I know it may seem like overkill when you're first starting out, but QB is universally known by CPAs, easy to find support on and easy to use. It will allow you to track your spending, clients/customers, income, expenses and do taxes really easily. You can also do payroll through QB for an additional yearly fee. I use it and love it. I can email the file to my CPA to work on and he sends it back to me.
Keep all business and personal stuff separate. I use a business credit card (through Citicards) and put all business expenses on it. Don't commingle accounts. Period. Don't do it. The LLC won't work to protect you if you commingle accounts.
The bottom line is that finding a good CPA will be worth the time and money. Find one that works with small businesses so the fees will be reasonable.
If you want to chat more, feel free to send me a message.