1) some of the altcoins have some online wallets similar to blockchain.info, some of them have multicurrency wallets that you can install on your device like JAXX and some of them have SPV wallets that are small and you can run them much easier than their full wallet.
i have never used the online wallets so i can't help you there.
never used JAXX either but you can check this board and ask around:
https://bitcointalk.org/index.php?board=37.0but SPV wallets are what i have used:
bitcoin + litecoin + Reddcoin: have Electrum (separately)
bitcoin + Dogecoin: have multibit
2) check out coinmarketcap.com and search the name of the altcoin in there. then click on the market tab to find where the coin is being traded.
try to only use the good exchanges such as poloniex, bittrex, kraken, btc-e, and also others that are small but still good: cryptopia, c-cex