Confusion before going for hair transplant. Should I stop using Minoxidil?

You need an examination and an understanding of what is possible with surgery and medication.  You need to understand what is possible with a hair transplant surgery.  Medications such as Propecia or Rogaine will NOT affect your surgical results, but it may help with your existing (non-transplanted) hair.  You and your doctor can decide the overall treatment plan which may or may not involve medications.

It is very difficult to comment without seeing your pics but in my opinion, you should keep on using minoxidil  even though it is just increasing the time period of hair on your scalp. As it will help to decrease the requirement of grafts right now. You can have a limited number of grafts now and then if the baldness will progress, then you can have a second sitting at that point of time. This way you can end up with better results in long term.

Many men use minoxidil after a hair transplant. In fact, many different hair growth strategies can be used including minoxidil, finasteride, laser and PRP after a hair transplant. These treatments don't work in everyone but may help a proportion keep existing hair. If you wish to use minoxidil in combination with a hair transplant, be sure to speak to your surgeon. Most surgeons advise stopping minoxidil 5-7 days prior to surgery. It can be resumed 5-8 days post op.

Your
biggest enemy is the progressive balding that you might have in the next 5 or
so years. Minoxidil is not the best drug for this problem. Before
you undertake a hair transplant, you should have your doctor try the drug finasteride on you for one year. Get
Bulk Measurements of your hair to determine the degree of the progression or if
you successfully stopped or reversed it because you need to get insights into
your immediate and long term future. If you are developing a more advanced
balding pattern which the Bulk Measurements will show over a one year time
frame, then you and your doctor need to develop a MASTER PLAN.