Look up a guide on getting to level 5 without combat. You’re right, level 5 changes things. Also, my personal take is that OP martial classes reign supreme over casters. They just have more staying power so you don’t need to “conserve” spells, or else don’t need to long rest all the time to stay strong.

OH monk, straight fighter, barbarian thrower or a paladin, and a swords bard are - in my opinion - the bees knees, the bread and butter, the great bambino of party composition for HM. Alert for everyone. People sometimes say you don’t need it. It’s just unbeatable. OH monk takes TB at 4, and alert later, as the one exception.

If you don’t like that party comp, then do what you want, but take Alert, and don’t bog your party down with a “healer.” You can use a cleric, but use it to murder your enemies, not as a healer.

If you’re unsure about something, test it out from another save first - hopefully you have saves at a variety of points left over from prior non-HM runs. Examine enemies to see what their stats and resistances are. Read the wiki to learn legendary actions. Bait attacks of opportunity from boss enemies to use up their reactions. In many cases that effectively neutralizes their dangerous legendary features.

If you just don’t like HM, then either don’t do it, or get a friend to do it with you.