Can I make my homeade wine in a sterilized 2.5 gallon plastic water jug,it has a spout so i thought i could open it a little bit to let the air out....should I?
AND ....How much Yeast,Sugar and Water and Grape Juice should i use for it???

Glass works alot better, but the water jug should do. It could leave a bit of a taste to the wine though that you weren't hoping for probably. You need to take the cap off of the jug right away! Put a balloon over the spout instead. That way, you can just deinflate the balloon. You don't want any air getting into your wine, but as fermentation occurs CO2 is released, and the jug needs room for expansion. If you leave the cap on it will eventually explode.

For every gallon of grape juice, I put in half a packet of yeast (it must be properly activated in lukewarm water!) and 3 cups of sugar. You need to experiment an find the tatse you like though. Cheers.