I'll try to help the best I can

Income Taxes
I figure 30%. It's easier if you already have an idea of what you'll make from experience, generally I find it easiest to put 30% into a savings account that accru's interest. I actually charge 30% more than what i need on a project just to cover taxes, this way I don't have to worry about it on a yearly basis because it's included into my hourly rate. Also remember that if you dedicate part of your house/apartment you can claim a percentage of all your utilities and rent on your taxes. Better yet, go to a CPA

Domain Name Register
Do some more research. You will find cheapest is not best especially in the hosting field. You can register a domain name anywhere basically but find a good host. Do the research yourself because if you ask for help you'll get 500 replies and be no closer to a good host. Consider total cost here, not just monthly. Total cost will include down time, your time for fixing problems, etc.

Hosting Server
Make sure you consider the cost of an internet connection here, simply because ADSL or regular cable will not work for you. You'll need a static IP and high upload speed. Most "high speed" internet is only high speed downloading, uploading (which is what a server does) is MUCH slower, sometimes only 64k or 128k. Just find out before hand, it's probably cheaper to host somewhere else. Don't forget to include your time for maintenance and updates because if you don't, you'll get hacked.

Office Supplies
Minimal office supplies required. Not even really enough to consider.

Marketing
You also need to decide who your audience is. Local or internet? With local business you get the (great) benefit of word of mouth advertisement as well as more loyalty. With internet business you're going to work for cheaper rates as well as clients who will decide simply not to pay you, however you have a much larger audience and more clients to choose from.

Postage and Shipping
I use e-mail for everything. I've only sent a few letters, and they were letters from attorney's. My attorny paid postage.

Telephone
Agreed.

Accounting/Legal
Do I need an accountant if I can figure out my own finances? What about legal? Yes and yes. Period. Your specialty is web services, theirs is legal and money services. They will save you money just like you would save someone money who doesn't know anything about building a web page. Remember, your time is money -- you need to spend it working for clients.

Travel
Again this depends on your audience. I generally make clients pay for travel expenses anyway.

Office Furniture
Never hurts to put something back for this because you will always need more, eventually.

Dues & Membership
This would be for things such as TechNet (on the technical end) or maybe some group or forum where you pay a membership to recieve useful resources and help. A lot of these are well worth the small membership, seriously consider but do your research before joining.

Licenses
You could call your local city secretary and they could point you in the right direction. I live in Texas so I'm no help here

Health Plan / Medical nsurance
If you will be providing yourself and family with insurance, put the monthly cost here.

Disability Insurance
Well if you get disabled somehow, you want to eat, right?

Retirement Savings
Totally depends on your retirement plan. How much do you save per month for retirement? any? Find a financial counselor and get a plan down. Call CitiBank, they have some good ones.

Multiply by 12 to get yearly OVERHEAD
Multiply the total of all the above monthly costs by 12.