Won't do a description of all the items, the video's worth 18 minutes of back and forth.
biggest surprise I got was how strong food can make you, duplicating your strenght based on just some multipliers.
Ads are great if you use them for money in the latter stages.
Offline helps you build up to 6 hours worth of money, that or find a balance between your army and mobs to the point of leaving AFK your phone for the night. you'll get a lot of coins.
Artifacts are good, but overplaying will demotivate you and you'll uninstall it.
Don't spend red gems on anything other than a 7,000 red gem key, they unlock divine treasures.