Let's say I am an holder (min 3 month)
In this case, you can buy cryptocurrencies from binance and move it to a noncustodial wallet, use a reputed noncustodial wallet, there are many fake ones. Not you key not your coin, that is why you can not leave your coins on custodial exchanges.
The altcoin I found are not listed in famous one like Binance. They have really low market cup: 100k.
The reason why such coins are not listed is because their marketcap is too low, only buy altcoins with high marketcap, looking for the first 50 to 100 Altcoins is better and still be careful. Do not buy low volume coins, they are shit or almost dead or dead coins.
So I would like to understand if the exchanges are good or not.
There are many exchanges you should not trust, do not trust exchanges listing low value coins, there are possibilities that you will see the coins today trading while it is delisted tomorrow. Also, people often lose to this type of coins, do not trade such coins or your will likely lose. The chances that you will lose is more than 99..99%.
How should I interpret the volume and liquidity values for the exchanges?
There is no much about this,. What that will likely happen are:
1. The coins will not be able trade at expected limit order
2. Another demrit is that, for example, if the coin price is $1, you trade it with market order, it could be filled at $0.5 or lesser in which you will lose ffrom the beginning of selling if the price has not much risen.