First off, as you start you choose your character... what you look like DOES NOT MATTER. it doesn't change anything about your effectiveness in the game - just pick a skin you like and go forward into your adventure!. Keep in mind, the game offers the ILLUSION of choice in quest dialogues, where you think maybe if you choose one or the other response to an NPC it will change the course of the story... wrong. it doesn't matter. It could matter for the fate of those NPCs you are working with, but it will not change the quests you do or the story path in any significant way. You will in the end get the same rewards, so just pick whatever suits you. So don't agonize over wrong choices along the way, they are just for roleplaying purposes for fun and will not change your path to the end of the story!
Do not hoard your purple dice... So many times I see new players not summoning with their free purple dice they accumulate, and I always suggest they just go forward and use them all. this will give you those epics and rares that you need to build balanced teams to progress content! Don't hoard! And duplicates pulled give you currency that allows you to boost artifact levels and purchase new artifacts... NOT summoning is really foolish and slows you down! Sure, you can save your orange dice, but i'll talk about that more later in this post.
Teambuilding: like I said with the purple dice summoning point, you can't really build a balanced team (tank, healer, debuffer, 2 dps) without actually summoning heroes... but basically you want to try and build a balanced team as you start out. horrus is a free fire tank and you get heksandra for free immediately; you have your main character (MC, traveler, whatever you want to call them), which is useful early to mid game, as they can swap elements for various teams and purposes... So fire/poison to start.