What is the right sequence or timing to buy and sell BTC?
When BTC drops, then sell all alts to buy BTC, when BTC goes high, then sell BTC for alts?
How many percents do you put aside for long-term HODLING?
In normal circumstances, there is no actual time to say "this is the best time to buy/sell bitcoin". Because it is a digital trading currency, then the rule of " buy low and sell high" comes to play, to avoid much losses. So, holding for a long run is a strategy that is used by investors who are really not into trading, but only for investment.
The simplest way not to be too concerned about the volatility of the cryptocurrency market is to invest in long-term potential good coin. The best time to buy depends on a lot of market factors so keep an eye out for your own investment.