how many different coins i will buy for trading?
It actually depends on how much budget you have for trading.
is it good to buy and sell 1-6 different coins or just stick to 1 kind of coin?
If you got more fund then surely you can go for few coins but don't invest in more than 5 to 8 coins because quite difficult to time the market in day trading.
what coin and what was the best coin that i can be hold for a long time that give me good profit. can i have your suggestion, thanks and gobless ! 
I can suggest you which is one is good for you but can tell you about my picks. I have NEO, GAS, IOTA, ETH, LTC, NEM, Waves and few other coins along with bitcoins.