Yes, you can claim all allowable deductions, such as your Exemption and your Standard Deduction (or Itemized Deductions).
Yes, sales tax, charitable donations, and medical costs in excess of 10% of your AGI would be Itemized deductions. As Critter points out, if your total Itemized deductions are larger than your Standard Deduction, that would give you a larger deduction.
Your AGI is $100,000. That comes before your exemptions and Standard Deduction/Itemized Deductions.
If your total "taxable income" (Line 43 of your Form 1040, which is AGI minus exemptions and Standard Deduction/Itemized deductions) falls in the 15% tax bracket, all of your capital gain will be taxed at 0%. If your "taxable income" is above that, only the portion that is above the 15% 'regular' tax bracket will be taxed at the long-term capital gain rate of 15%.
If you live in a State that has income tax, most States tax long-term capital gains at regular rates.
