even though that's a translation that basically keeps the meaning of the sentence intact, it changes its composition: there's no subordinate in your sentence, while the "was" in the german sentence is there for that reason, to link the two sentences: "I make everything that/which you like"
Möchtest is subjunctive, so if I had to hazard a guess, I would say that möchtest is used because "I" am uncertain or doubtful of what it is exactly that "you" want. That's my best guess. I came to this conclusion by borrowing subjunctive rules from French and Spanish.
Something I've just realised that adds to this problem is that in German, subordinate clauses are separated with a comma, whereas in English, we don't use them for that at all; commas are used to separate co-ordinating clauses of equal value in the overall sentence. We tend to forget that punctuation does different things in different languages - Thanks for the hint!
Does the German present tense translate to the English present, present progressive AND simple future tenses? The alternate translation that Duolingo provided to me was: "I will make everything that you like". Additionally, isn't "möch-" the subjunctive tense stem for mögen? If so, then shouldn't the translation be: "I will make everything that you would like"? Do any of you know the rules for employing the two subjunctive (Konjunktiv) tenses?
1) Depending on the context, the German present tense can refer to the present or the future. Also, Standard German doesn't have separate forms for the progressive and the simple aspects in the various tenses - this grammatical concept simply doesn't exist in Standard German.
2) Yes, "du möchtest" means "you would like". Basically, it's a more polite way of saying "du willst" (you want). "Du willst" could also be used in the German sentence in the exercise without changing the basic meaning. I think the appropriate English translation would depend largely on the context here. For example, if a man was pointing a gun at you, I don't think you would say "I'll do anything you would like!" Rather, you would use "want" or "like". English is not my native language though, so I maybe I'm wrong.
The main clause is "Ich mache alles" ("I do everything" in this case "I'll do everything" really because it refers to future actions) and the subordinate, here a relative clause, describes 'alles' (everything) with "was du möchtest" ("that you would like") You may want to check out this link, look for 'indefinite nouns or pronouns' https://www.lsa.umich.edu/german/hmr/Grammatik/Relativsaetze/relative.html#WerWoWas