but keep all gold till Events is a little dangerous because maybe someone attacking and loot your gold, isn't it?
There is actually almost no real danger because if you follow the strategy you will be stronger than everyone within your battle value range.
Imagine you're level 16 with all the best items for your level, however your battle value is 101. The normal battle value for levels 15 through 20 is around 300-400. Consequently, all the people that are around your level won't be able to attack you because they are not within your battle value, and all the people that are eligible to attack you are low levels (which you will always defeat because even if they have good stats, your items are superior and you will win).
There's also always the chance that there are other people who are also doing what you are and they might attack you and win. And if that is the case, you should try to obtain a battle value in which you would be the strongest and no one would attack you.