I think the best reasons to buy an altcoins is mainly to consider their project whitepaper and dev team because there are lots of altcoin with similar project and shady developer. However there are also many project that doesn't seems to help making human life easier and mainly focusing in maintaining their price after ICOs and after entering the market.

High volume doesn't mean that coins will last long or the project will continue in the long term, if you're a short term trader then this might help you however if you're a long term investor then this doesn't make sense at all since coinmarketcap volume only shows the last 24H.

You should know that a rise happened when the price is pumped, if you're waiting then you should underline how long you will wait until you want to buy. Is it after the correction? Is it when the price created a new high? Most people tend to buy when the uptrend already over and considered a new dowtrend as a corrections. Its better to follow the whales then to swim against it.

You can't predict a pump and dump just by looking the chart, a dump in lower 5M timeframe doesn't even mean a thing when you consider 1D volume, each chart has their own volume and volatiliy. You should consider what kind of investor you want to become, is it a trader with lower timeframe (5M,15M,1H) for trade or an investor with higher timeframe(4H,1D,1W). For the record, if all you do is waiting when the price is pumped and dumped, then its better to wait in the sideline and not try to invest at all because there is no perfect time to do an investment unless you already created a plan to overcome the lack of information.