In the US tax system, you cannot "write-off" capital assets. You have to depreciate them, with very specific exceptions. So while you may be purchasing $4500 of equipment, your deduction may be significantly less. For example, computers are depreciated over the period of 5 years, so if you bought a $1000 computer - you write off $200/year until it is completely depreciated, not $1000 at once.
There are exceptions however, for example - IRC Sec. 179 is one of them. But you should talk to a tax adviser (EA/CPA licensed in your State) about whether it is applicable to the specific expense you want to "write off" and to what extent.
Also, keep in mind that State laws may not conform to the Federal IRC. While you may be able to use Sec. 179 or other exceptions and deduct your expenses on your Federal return, you may end up with a whole different set of deductions on your State return.
And last but not least: equipment that you depreciated or otherwise "wrote off" that is later sold - is income to you, since depreciation/deduction reduces basis.
Ah, and keep in mind - the IRS frowns upon Schedule C business that consistently show losses. If you have losses for more than 3 in the last 5 years - your business may be classified as "hobby", and deductions may be disallowed.
But the bottom line is that yes, it is possible to end up with 0 tax liability with business income offset by business deductions. However, not for prolonged periods of time (not for years consistently, but first year may fly).
Again - you should talk to a licensed tax adviser (EA/CPA licensed in your State). It is well worth the money. Do not rely on answers on free Internet forums as a tax advice - it is not.