I hope others will chime in, but I'd personally avoid third party sites and book on delta.dumb. If you need to call and talk to DL web tech support because of problems/errors with the DL website, they shouldn't charge you the phone ticket fee. Try to click on advanced search (or access book a flight from the top drop down menu, not the left hand side) and enter your airports including connecting points. However, be careful that delta.dumb doesn't try to charge you extra as if you had stopovers (defined as over 24 hours or first possible connecting flight for international).

Are you trying for an award ticket (miles) or a paid ticket? If miles, it would be wise to read some of the material on FT first. Reading further, since you're asking about MQM, I would assume paid tickets and since you ask about exit rows, I would assume coach.

In this case, you should check the general advice here or ask the experts whether it's wise to buy your tickets so early. On some routes, prices frequently tend to decrease closer to the trip. Also, don't forget that you'll be giving Delta the use of your money for almost a year and there will be schedule changes.

I think as Silver you can select exit rows in advance for free, including a companion, but I'm not sure with all the changes.

If your itinerary involves any non-DL flights (in this case, AF operated or share codes), be very careful about which fare codes earn 100% MQM. If you search by fare class (i.e., H or higher but you should start with L or higher to see the cheapest options), you can see the fare class as you go when booking, but you have to click further to see the exact fare code and its rules.