I need advice on alternative currencies to purchase before btc rallies above 8000 usd.. anything among the top 100 coins on coinmarketcap will do just fine
Looks like you answer yourself, anything among the top 100 coins on coinmarketcap could be a good option, is smart to invest in the coins with biggest market capitalization, because since the coin has a big market then is hard for it to die.
But if you want specific recommendation you should hold some LTC, ETH and BCH