Gold is the most important when you unlock your tier 5 troops. The amount of gold that you will need to train and heal tier 5 troops is too high. You will run out of gold very fast so save all that you can . You will need all.
When you create a new account in Rise of Kingdoms, your usage of gold will be minimum. You will spend some on technology, building but that is nothing when you compare it to healing and training of Tier 5 units. When you get Tier 5 your gold will start to melt. That is why a lot of tier 5 during KVK will ask for gold. Save all gold you can.
When you unlock your tier 5 troops you will need to have a farm account.
With farm account, you will be able to farm normal resources. You want to farm with the main account gold simply because you will have much better gathering commanders, technology for gathering and to avoid transfer taxes.
Zeroing city – Well first and most easiest way is to zero dead city. Because you do not need a lot of gold until you get to tier 5 units, they will be full off gold. Just scout them and if they do not have a lot of troops just loot them.
I gold around 600m of gold from 2 dead cities, yes I lost some troops but its 100% worth it. If the city is too strong then ask a strong player to help you and you can share the loot.
If you have a lot of gold you must be careful in kingdom vs kingdom. You will be a big target.
Farming- well this is boring. As I mention farm gold only with your main account. You will have a better gathering commander and technology for farming. If you are looking at how to optimize and get a lot of gathering buffs you can check our farming guide.
Resources items- you can get resources items in events and in a merchant shop. My advice is to not use resources items if you have gold in storage. More gold you have the higher target you are. Big spender will always look for a city with a lot of gold.
One more time My advice is to keep all your gold and do not donate it if you are free to play and you do not have tier 5 troops. YOU WILL NEED A LOT OF GOLD WHEN YOU GET TIER 5 TROOPS.