Here are some tips for completing the Gauntlet with an SS rank.
These are observations I made along the way when playing it. Some tips are factual, but some may depend on your style of gameplay, thus the two following sections.

• The most important one : you can retry the song individually! If you are about to fail: press Escape and click "Retry". It will not take you back to the beginning of the gauntlet, but to the start of the song ! Not only that, it will forget every "Hit", "Miss" and "Overclick", modifiers you got, Glass broken and Barrier lost. However, you do not get back the GC (Gauntlet Currencies) you used on rerolls.
  
• Yu & Mei work differently in the Gauntlet. If you complete her progress bar, you get 3 Benedictions. So if you complete it twice, you have enough to get through Yu's one without bad modifiers. However, you will not get more modifiers on Mei's bar after completing it once, just the Benedictions.

• If you want the SS Rank specifically, then buy the first item in priority, as it boosts "Perfects", the only thing you should get anyway in the Gauntlet
  
• Remove the 180 and 160 BPM at the start, unless the others bore you too much ;)
  
• I recommend having (not in order) : 1 or 2 Seer, 2 or 3 Glass, 2 Stamina, and the rest in Sap/Needle/Perception/Guardian. Only take Barrier if you took Doom.
  
• Always reroll for Whip, or take 1 or 2 Nitros, not more as it will be difficult to see Mines, Fissions and Holds if you have to take them.
  
• When choosing for a *** modifier, I recommend choosing (from most to least priority):
  
  • Bewitch : because it is only impacting the duration of the song
    
  • Fission : because with accumulated Glasses, you should be safe hitting the notes
    
  • Doom : because you should not miss anyway, but be careful, you can't retry the song if you lose ! (I think)

Let me know if I made a mistake somewhere or if you have suggestions