How Many FUE Grafts
Your donor supply does not seem excellent from the photos as your scalp can be seen through your hair. It will be difficult to get 3,500 grafts. Most of the time clinics that advertise procedures such as this cut the 2-4 follicular unit grafts into singles to get you the "number of grafts promised". My experience has been that when grafts are cut, their survival rate decreases. You also need density, so having bigger grafts is likely what would benefit you the most.
There are excellent hair transplant doctors in the UK, one of the being Dr. Farjo. I'd recommend you visit with someone local before you go all the way to Turkey.
A great doctor can make you look great with only 1000 grafts. A bad doctor will make you look worse even with 6000 grafts.
I get that you want reassurance and this is one of the resources available to you to hear doctors' opinions.
You can pick and choose the answers below to satisfy your needs.
In the end, the number of grafts or the type of surgery (FUE, FUT, Artas, Neograft) does not matter!
If you have a great doctor who understands your goals and you trust your doctor to carry out your goals to the set expectations, you will be fine.
Example: A great doctor can make you look great with only 1000 grafts. A bad doctor will make you look worse even with 6000 grafts.
3500 Grafts planned in Turkey
You have a Class 6 balding pattern which generally takes about 6000-7000 grafts, obviously in more than one session. 3500 grafts is a reasonable start. I have heard some complaints about transplants in Turkey, so see my web post below as wrtten by a patient to me
What to expect on your hair transplant surgery in Turkey
You must have realistic expectations. Because of your less dense donor you might not be able to have 3500 grafts extracted. I could say about 2500-2700 grafts may be available. In this case, you must select a good doctor who can get the best outlook out of your available donor. Consider that the most important aspect here is natural looking result, and not density. In this case, your doctor should focus on creating a good hairline, denser frontal hair and less dense crown. This will greatly change your overall appearance, and would look natural. If you focus on or expect filling the whole bald area, you will definitely be disappointed with the results.
Another main point to consider is selecting a good doctor/clinic in Turkey. As you now know, there are many hair transplant centers in Turkey and more are coming up. Do your research well. Do not go for the cheapest offer, neither the most expensive. Go for a very qualified and experienced surgeon.
All the best.
Planning for FUE
From the photos you sent me it appears that you do have decent donor area. However your age plays a factor here as well as ancillary treatments you may or may not have tried.you do have a fairly extensive hair loss and so your expectations of the final results must be clearly defined (if that is even possible).
Hair transplant or not.
From the pictures that you have shown you do not look like a good candidate for any type of hair transplantation. Your don or area looks especially thin and you would be trying to "rob Peter to pay Paul" which ends up with an overall poor look.
From the pictures it looks like you could be a stage 7. That many grafts could be tricky to achieve unless they cut up the grafts. But of course nothing would substitute an in person exam. You should find a local doctor.