Hi Pam. Part D (Rx Drug) will impose a penalty for waiting so sign up when you can.
As for retiring, believe best to work as long as comfortably can. An extra year or three means more funds saved and no retirement money spent. You can always fiund an IRA if no retirement plan at work.
Not clear if you are considering remaining with same employer or new job. Your present employer may have you take your pension which likely will not increase beyond normal retirement age.
As for Social Security it increases about 8% per year delayed which you can do to age 70. For five years that means the benefit is 40% greater than 65 plus it's indexed so future COLAs are applied to a higher base. Decision on timing is whether you need it to live on plus your medical history. If your parents died early or you have or had cancer or other life shortening diseases, better to take earlier. It takes about 15 years to break even so if one lives longer they get more. SSA gives the monthly benefit at each future age.
Finally if your are or were married you may be able to claim your spouses SSA benefit as a spouse. Then once you reach 70 for example you can file for your own, higher, benefit. This can give you some SSA as a spouse and then collect your own higher benefit later. The SSA law is quite complex. Others can help including SSA who will ask whether you were ever married. This spousal benefit applies if one is divorced or their spouse is deceased.
Good luck. Hope all this helps and pretty impressed with the knowledge of BF members.