Study some technical analysis and use support, resistance and trendline break on higher timeframes like Daily (D) or Weekly. This timeframe is good for longtime hodlers like you. Sell if the chart is about to go down and buy at the bottom. Follow your plan 100% and dont get emotional.
This might help but not accurate , it will give you some basis whether to follow the pattern as it will give more ideas what would be the next outcome, but with your questions OP, it's really hard to say or predict when the dump will happen as crypto industry is full of speculations and because of that, emotion needs to be controlled properly to avoid wrong decisions, just aim for long term hold if you are in an investment type person.
Yeah, a very good one. Daily chart most especially is the best for long term holders and adding to what rommelzkie have said, I would consider the OP or anyone in his shoes, learning how to make use of the moving averages, bollinger and then reading the candles to be able to make some decisions when holding for long term.
There are plenty resources online and they can easily direct someone into learning how to do all of that. Trend following is a pattern every long term holder uses, and that should be of great help.