A violin transcripton was published in 1944, while the first flute version was published in 1948.
Yes, the triplets after the repeat should be triple tongued, and that section should be "forceful".
Practice your long tones, lots of support, and you should be able to get the D4. I use the T 3/45 C#/C fingering. Also on the triplets up to the D4, use a harmonic Bb for Bb3 for easier fingering.