A. You can use the GPE prep materials on the Blackboard system. Additionally: When you do the sight-singing on the GPE, you can use any system (solfege, numbers) or no system (singing on la), as long as it is accurate.
I think learning the interval directly, and by comparison to the major scale, instead of by comparison to familiar tunes, is quicker and better. You can do whatever works.
Each interval name has two parts: the modifier (major, minor, perfect) and the number (second, fifth). To practice the intervals directly, sing the first note on the modifier and then leap to the second note to say the number. For example: (on C) "perfect" (on G) "fifth".
For sight-singing tonal melodies, separate the task into two stages: 1. tonal indexing: identify the scale degree (with numbers or solfege syllables) of each note in the melody 2. after establishing the key in your voice, sing the melody using scale degree numbers or solfege syllables
To practice the tonal indexing step, write out a string of noteheads, with scalewise and leaping parts, like a melody, without a key signature. Then practice choosing a key signature and identifying the scale degrees. Then sing it. Then change the key and give it a new set of numbers for the new key. Then sing it. This isolates the tonal indexing skill so you are faster on that when you go to sight-sing a melody.