If you take a lump sum from the pension plan then it will be subject to income taxes and the 10% penalty unless you are considered permanently and totally disabled. If you are receiving social security disability benefits then you would meet that definition. If the pension plan is paid to you over your lifetime in monthly payments instead of a lump sum then those payments would also be exempt from the 10% penalty tax.
If you take a lump sum to payoff your loan then depending on the amount it could push you into a higher tax bracket. Another option would be to have the lump sum directly rolled into an IRA. Then you could take periodic distributions from the IRA to make loan payments or to make additional payments. This strategy would spread the taxes over a number of years. If you meet the disability exception, then distributions from the IRA would also be exempt from the penalty tax.
You could also request that the 401(k) be rolled over to an IRA. With an IRA you can invest in a variety of investment vehicles similar to the 401(k) investments, including age-driven mutual funds.
Yes, you should engage the services of a financial advisor. There are many firms that can assist you including Merrill Lynch. You may want to meet with at least 3 advisors at different firms to determine which one is most suitable to you. Some firms have additional fees that apply if your accounts do not exceed certain amounts, so that is an important question.
For the tax filing you would engage the services of a tax preparation firm.
If you withdraw $50,000 a year then that will push you into a higher tax bracket and you may have to pay a tax rate of 25% on some of the distribution. You might want to withdraw a lessor amount and merely make additional principal payments which will reduce the number of years that you will have to pay.
If you invest in a self-directed IRA then you can purchase stocks, bonds, mutual funds and other types of investments. You are not restricted to bank CDs.