New to the game

Just started this game because I heard the story was incredible and the locations looked gorgeous. Didn’t know it would be this difficult. Caught pokèmon that looked cool and got my ass beat by some trainers since they have op stuff. Currently cant get past Marianette or whatever because I refused to catch the pokèmon that didn’t look good. Any tips on how to even do this without having to research and prepare for every opponent? Since that defeats the purpose of surprise n stuff.