You do know that the Sicilian is the most theory intense line against e4 matching e5 as a response. Much simpler to do the Scandinavian or Pirc opening as black. I play the Sicilian myself but there is a lot to know even if you have your own pet line because both sides have lots of viable options. I also play the Dutch which is fun and has a smaller amount of theory, but enough crossover to be useful with other d4 openings. For main opening as white any of d4 or e4 will require enough theory to be studied if London is not played. C4 does mean a decent amount of theory will need to be known, but maybe the Botvinnik English might provide a solid grounding. Your friend might just want to try out all the main ones and see what they like. Maybe they will study one they like more than just any opening that is suggested.
Best variation of the English opening/Sicilian defence for a beginner
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Well, my friend is actually intermediate, but he hates the very existence of the openings and hates studying theory. He often suffers from this because his opponent's already know some openings and use their superior theoretical knowledge to get an upper hand over him. He knows basic london system and modern defence...yeeeeah...idk who decided to teach him THIS repertoire, but he basically hates both of these openings. I thought that english and sicilian dragon would be great option for him since they both are quite similar and easy to learn(if you don't try to abuse transpositions or don't try to enter najdorf) and, most importantly, are unfamiliar to opponent and cut back their theory, making a fight even without much effort. So the question is, which system is best for this purpose? And what to play against D4 and the polish? I was thinking about old benoni..