Retirement

Yes remove this deposit from your IRA account, you will be over the limit and have to pay a penalty to the IRS.  Talk to your financial advisor as to how to go about doing this.  Keep a detailed record of the money going in and the money coming out.  This needs to be done by year-end

Yes the backdoor IRA strategy will work for you. One note of caution is that there is potential this strategy will be limited if the version of the Build Back Better Act that is about to go to the Senate for a vote passes. Consider making the move soon as some of those provisions will take effect Jan of 2022.

Additionally note that there is a possibility of the side door Roth if your plan at work allows non deductible 401k Contributions. Reach out if you want to discuss further

For 2018, the tax rate on the employee portion of Social Security is 6.2% on wages up to $128,400, so Social Security tax withholdings should not exceed $7,960.80. Medicare tax of 1.45% is withheld from all wages regardless of amount.

On Schedule SE for 2018, self-employment tax of 15.3% applies to earnings of up to $128,400 after the earnings are reduced by 7.65%. The 15.3% rate equals 12.4% for Social Security (6.2% employee share and 6.2% employer share) plus 2.9% for Medicare.

If net earnings exceed $128,400, the 2.9% Medicare rate applies to the entire amount. One half of the self-employment tax may be claimed as an above-the-line deduction on Schedule 1 of Form 1040.

In 2016, there is no increase in the Social Security wage base of $118,500. The Social Security tax rate on employers and employees stays at 6.2%. The Medicare tax rate on employers and employees stays at 1.45% on all pay. BUT...
In 2017, the Social Security wage base is raised to $127,200. The maximum amount of Social Security tax a taxpayer will pay in 2017 will increase from $7,347 in 2016 to $7,886.40 in 2017. An increase of $539.40.
in 2017, the Social Security tax rate on employers and employees stays at 6.2%. The Medicare tax rate on employers and employees stays at 1.45% on all pay.

IRA (Traditional or Roth) Deadline to establish the plan and the Deadline to fund the plan is April 15th of the following year.
SEP IRA - Deadline to establish the plan is the due date of the tax return, including extensions and the Deadline to fund the plan is due date of the tax return, including extensions.
Simple IRA - Deadline to establish the plan is October 1st of that year and the Deadline to fund the plan for the Employee contributions must be withheld from pay by December 31st and remitted to the investment firm as soon as reasonably possible and the Employer contribution must be made by the tax return due date, including extensions.
401-K or 403(b)- Deadline to establish the plan is October 1st of that year for safe harbor plans, otherwise December 31st of that year. Deadline to fund the plan for the Employee contributions must be withheld from pay by December 31st and remitted to the investment firm as soon as reasonably possible and the Employer contribution must be made by the tax return due date, including extensions.
Defined Benefit Plans and Profit Sharing Plans and Keough Plans must be set up by Dec 31st of that tax year.

On March 1, 2013, the Treasury department will stop mailing paper checks to Social Security recipients. Retirees will be required to choose to have their Social Security payments either directly deposited into a bank or credit union account or loaded onto a prepaid Direct Express Debit MasterCard.
New Social Security beneficiaries have been required to choose an electronic payment option since May 2011, and approximately 93 % of Social Security and Supplemental Security Income payments are already being made electronically.

The 2012 social security tax rate is 6.2% of your earnings (or 12.4% for self employed tax),The employer will still need to pay 6.2%
The 2011 Payroll Tax Cut temporarily lowered the social security tax rate for the employee to 4.2% in 2011.The employer will still need to pay 6.2%