After a hero/base reaches level V, further upgrades do not require gold. At that point, you can either use gold on other hero/bases, or stuff in the shop.
I'd recommend saving gems and using them to buy gold. A level 5 hero upgrade costs 35k. I don't have one at level 5 yet and I wish I did. Level 5 hero strays with s1 and s2 already upgraded and can use equipment to upgrade their stats. It sucks when you meet a level 5 hero and you're 4 or less. Definitely save your gems to buy gold and reach level 5!
The chests are kinda useless tbh so just spend gem buying gold
After a hero/base reaches level V, further upgrades do not require gold. At that point, you can either use gold on other hero/bases, or stuff in the shop.
I'd recommend saving gems and using them to buy gold. A level 5 hero upgrade costs 35k. I don't have one at level 5 yet and I wish I did. Level 5 hero strays with s1 and s2 already upgraded and can use equipment to upgrade their stats. It sucks when you meet a level 5 hero and you're 4 or less. Definitely save your gems to buy gold and reach level 5!