Repeat words in tags?

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Compound keywords should not be used unless they represent common phrases. "Gold glitter heart" is not a common phrase in English. If a Buyer searched for "gold heart", your asset would not match if you had entered "gold glitter heart".

Check here for guidance: https://helpx.adobe.com/stock/contributor/help/titles-and-keyword.html

You should repeat the relevant keywords from the title, but as compound keywords are concerned, you should use those only, if they are commonly used as a compound word. Otherwise, it could be considered as keyword spamming.

So I would use “gold”, “glitter” and “heart”, but not “gold heart”, “glitter heart”, “gold glitter heart” …

You can fine tune your keywords later on, if you have doubts about the efficiency of your settings. However, if there are two million gold glitter hearts, don't expect wonders.

More on this: I'm often dealing with keywords the likes of: "makeup, make-up or make up; or skin care, skincare; or closeup, close-up, or close up." Should I pick one? Or two? Or all three? At times, Adobe will automatically suggest at least two of the possiblities, so I'll go ahead and select both as recommended, along with my own that Adobe doesn't come close to recommending.

And there you have it. Two different answers so far. 🙂 Myself, I use my own judgement on each image. I often search my own contributor page to see if I can find an asset based on my keywords and I find that, in general, Adobe Stock seems to be very loose with the results. I might do a search for "blond hair," for example, and I'll find assets of blond people as a result. But I will also see results that I know very well did not include 'blond,' but may have included hair, so the results return redheads as well. 

You should use the keywords, both compound and singlke that a searcher would most often use. Use theese in the order of importance. 
Optimize your content for search with effective keywords at Adobe Stock

No, you would not need to repeat keywords in the method that you mentioned. I'm no expert on using keywords in Adobe Stock, but I think that would amount to spamming or attempting to game the system. Let some others step in to reply.