1) My favourites were 1* Sharan and 2* Layla. I used Layla for quite some time, the best 2* in my opinion. I even gave her emblems, but at some point she couldn't keep up anymore, and I had to retire her.
2) It's important to proceed with map missions, to conquer the outposts which boost food and iron production.
3) New players won't have many gems, and it's best to spend them on roster expansion. Not worth buying gems at this point, just collect the free gems from the vision tower and daily streak rewards.
4) Go on raids as often as you can, rewards give a lot of extra food and iron. Play tournaments, they help to fill the heroes chest and give extra rewards at the end. Level up farms first, food is what's most needed throughout the game.