Your kingdom approach is correct and should be your gold sink priority until all reach level 10 and you can start adding stars. Hopefully you are in a guild and already have bought dragon armour. Both of these will accelerate your progression significantly. A few other things you should consider.
Classes. Some hero classes are much stronger than others and should be prioritised accordingly. 250 wins with each class also provides a new weapon such as skeleton key. It takes a long time boosting class to 100 so share the love, bag the weapons then focus on the important ones. Titan, sentinel, runepriest, and sunspear are my favourites but you will have your own. Get all classes to 40 then boost the ones you use most.
Orbs. If you are enjoying gems and think you are in it for the long haul, save your blue ascension orbs as much as possible. If you ever want to forge zuul Goth you will need them. Wisdom orbs can be used sparingly when you have a troop worthy of the expense
Events. It is a good idea to buy as far as the weapons tier in most events. Raid, Invasion, Doom all have associated weaponry which may not become available again once the event is over.
Delves. At low levels, delves are difficult but do them daily if you can to boost renown, resources such as shards and the much needed legendary and mythic ingots.
Gem mastery. As you level up, you are invited to pick which mana you would like to boost. As you continue to boost, new weapons become unlocked, such as the excellent mang, which is a gamechanger for any new player.
Resources. Be frugal…don’t spend every gem, diamond you have at your disposal. Similarly don’t trait or boost troops just because you can. As soon as you do, you are guaranteed to find a great troop you can no longer boost cos you’ve just spent all ‘his’ resources on a troop you never use.
Gems are the main currency. Don’t spend them on pet food, keys, unnecessary armour or anything else. You will need them for events, wars sentinels, forging and so on. Again, be shrewd.
Soulforge. You need to unlock this feature to enable you to craft resources, including weapons and mythic troops. Do the associated Dungeon sidegame every day to get diamonds to forge resources in the forge. Your 1st mythic forge should be Pharos Ra in my opinion.
That’s about it from me. Look after resources and spend wisely. Choose a good home kingdom like whitehelm or Shenyang. Oh and keep a good stash of glory to spend on the troop and arcane stone packs in the weekly reward shop.
And have fun.