Unfortunate, there is no one solution for your problem. You have to handle each altcoin with their own wallet.
just use a erc 20 wallet . myetherwallet is the most famous one. or you can use any erc 2o supported wallets
MEW can only hold ERC20 tokens based on ETHEREUM blockchain. It cannot hold other altcoins like ltc, xem, xrp, etc.
I store all of them in exchanges, because im afraid i may lost my wallet someday, of course they should be big exchanges such as binance.
Not a wise idea. Exchanges are not wallet and you do not hold the private key so if they suddenly decided to close, your coins are gone.