Yes you can write off your expenses, meaning you don't pay taxes on that amount, not that you get the full amount back. So for any equipment you purchase, it is 100% tax-deductible, though the amount you can deduct each year is based on depreciation. If you have a home based business, what ever portion of your house is used solely for the business is tax deductible. So if 10% of your house is used for the business, 10% of the rent/mortgage, taxes, utilities, etc. There are special rules around phone service, that I just let my accountant handle.
However, if your are audited and the IRS finds out that you are not a legitimate business you can be forced to pay back all the write offs you claimed. Generally speaking, if you are not making income you're not a business.
As I am not an accountant, so please do not take this as legal advice, just some dude on the internet. You should consult an accountant and possibly an attorney before starting a business and/or claiming business expenses on your taxes.