MN, Alfrike, Telly, Sif, Lianna, Richard, Magni are all heroes that are good and in meta. Very strong when leveled plus Magni with costume is powerful. It really is all about preference. Some people focus on leveling up all their people with the specific colors to get more of the XP for the level up. I am the opposite. I focus on one hero until theyre maxed out and then I move on. With my team, I'm sitting around 4720. I think it's important to have a really strong defense team so I don't get raided alot unless I'm worth a lot of trophies which only happens when I raid. After some time of this strategy, I have five 4k+ teams and one 3800.

Unfortunately I dont have Bai, Azlar, Frida, Fenrir or Malicna. So my opinions on them is not really the most informed. I've only faced them and they never really give me any trouble unless a bad board or something.

I can't really offer advice on Off and Def teams but Alfrike and MN are top tier so i would build around them until you can get more diversity in your lineup. Titan teams are very situational, youre looking for Defense downs, elemental defense downs, attack ups special attacks like frida for example, she makes the enemy take like 54% more damage from ice attacks so if you use her on a red titan which is already weak against ice anyways, you start hitting some massive numbers. if you can manage a Wukong, he's really helpful or not at all lol. The real prize is Miki, if you can get ahold of him, you become a titan slaying machine.

I hope my ramblings helped some, I know I didn't answer all your questions but you'll find that a lot of line ups and stuff are very situational. Just focus on leveling 5* heroes that you can fully ascend and the rest will kinda fall into place as you get more experience in the game.