1. Yes. You can also verify exempt organizations here https://www.irs.gov/charities-non-profits/exempt-organizations-select-check
2. This is typical. The organization will sign a receipt showing they received the items but will usually not give a stated value. You are responsible for determining the fair market value; what a reasonable buyer would pay a reasonable seller for the same or similar item in similar condition.
There are several ways you can estimate fair market value. Try looking at other used furniture stores, or look at the Habitat store to see what price they put on the pieces, or check ads in Craigslist and eBay for similar items. You may want to print copies of ads for comparable items to keep with your tax papers in case the IRS wants to know how you determined the value.
You also need to know when you acquired the items and roughly how much they cost, or if they were a gift. You generally can't claim a value larger than the original cost, except under special circumstances. For example, if you have a dresser that your grandmother paid $49 for in 1960, and was given to you as a gift, then your maximum donation value is $49 even if it is worth more. (There are some exception but they don't apply to you if the recipient organization is selling the items to raise money.) Make a list of items you are donating with their present value, original cost, how you obtained them, and how you determined the present value. Keep this with your other tax papers.
If the total value is more than $5000 then you need a signed appraisal from a qualified appraiser, and you need to prepare a copy of form 8283 that lists the items, and is signed by the appraiser and by a qualified financial officer of the charity.
3. You can deduct the present fair market value, or your original cost, whichever is less. This is an itemized deduction on schedule A, so how much you actually benefit depends on your overall income and other deductions. Generally, most taxpayers will reduce their tax owed by between 15% and 25% of the value of the donations.
