Exepting coins which are top biggest marketcap, I dont think that investing in altcoins for a long time is the rigth way. You should trade them instead
You should always stay invested in some fo the altcoins if you think that currently they are very cheap and in coming time it could rise a lot like how btc has risen during this years. For rest of the amount you can also trade as per your wish but ensure some amount of your favorite coin you are always invested in it.