Not much to add to SGs comments. I am in a similar position, training for my second marathon. For an advanced plan, I would have expected to see 5 or 6 long runs of 20+ miles. I wouldn't be happy with two @ 20+
Midweek I will be including a medium long run (10 to 14 miles). This and the Long Run will have some mileage at MP. I did up to 10 miles at my target marathon pace for my 1st race.
I have about 3 local half marathons scheduled. Two of these will be raced (one 4 weeks out), and one will be in the middle of a long run - I will run this at MP.
Tempo runs - I do 5 to 6 miles at my half marathon pace. If I could only do this, or 5 x 1600m due to time pressures, I go for the Tempo session.
Regarding training on the flat, and living in a hilly location - I had the opposite problem. Its fairly flat here , and I was running a hilly marathon. I believe in getting your training race specific, and for me this meant driving a few miles until I found a loop that included steep climbs.