Hi and welcome to Just Answer!
So far - based on your information - following is your taxable income
FERS retirement $12,624
InterTek survivor benefits $ 7,011
Social Security payments: $20,644 - taxable part $ 2478
2012 Income Adjusted Gross Income (AGI) - $22113.
You will be able to deduct personal exemption $3800, and
if you are using standard deduction
If you itemize - following will be included
Real Estate taxes $5500
Real estate taxes paid in 2012 for past years $6100
2012 taxes due for same acquired property $ 2400
Total real estate taxes $5500+$6100+$2400 = $14,000
Medical Bills paid $ 2900 plus Medicare payments $1188 + Medicare Supplement $2246 = Total medical expenses
Deductible medical expenses $6334 - $22,113*7.5%=$4675
Total itemized deduction $14,000+$4675=$18,675
Because that amount is larger that your standard deduction - you will likely itemize.
So far your estimated TAXABLE income $22113 - $3800 - $18,675 - would be negative - and whatever were withheld $106 - will be refunded to you.
If you will have additional taxable distribution from your inherited Fidelity Traditional IRA - $20,000 will be your additional income - that will not affect your eligibility for social security benefits - because that is not earned income - so nothing you would need to pay back to SSA.
However - your tax liability will be different.
First of all - out of your Social Security benefits $20,644 - taxable part would be $20,644*85%=$17547
Plus additional $20,000 in taxable IRA distribution
So your AGI will be $57182
Your Deductible medical expenses $6334 - $57182*7.5%=$2045
Total itemized deduction $14,000+$2045=$16,045
So far your estimated TAXABLE income $57182 - $3800 - $37337 and your estimated tax liability is $7600.
- minus whatever were withheld $106 - and you will owe $7500.
You tax liability would be less if you have additional items to itemize - charitable donations, mortgage interest, etc.
Let me know if you need any help.