At the beginning of the game Seven.
During the game, you can have a unlimited numbers of cards in hand.
However, during your discard phase (before the end of the turn) if you have more than seven, you must discard as many cards to keep seven (except when a spell (enchantment) or a effect in play authorizes more than seven cards during this phase).
NB: Starting hand sizes can be modified during game variants, like Vanguard.
You should allways try to have the minimum amount of cards in your deck. The minimum for most formats is 60 cards.
60 cards
There are over 60 Magic The Gathering FAQ on WikiAnswers.
Rebound only works when the card is cast from your hand. So; You cast Distortion Strike from hand, Since you cast it from hand, exile it when it resolves, At the beginning of your next upkeep, cast it from exile, and since it was not cast again from your hand, it stays in exile, and doesnt effect anything again.
41
A lot
No matter the rarity of a card, you can only have up to four of that single card in a legal deck (besides basic lands, of which you can have as many as you want.) The only exception is the card Relentless Rats, which states on the card that you can have as many copies as you want.
not enough
90 and still more
Magic is played on many, many college campuses. To find out if there is an organization on your local campus one should contact the activities office. Since magic is so popular with college students, if your campus doesn't have a magic the gathering club, you should consider creating your own.
Booster boxes of magic the gathering can be picked up at most trading card stores. Or online at many gaming websites. Some that I have personally used are www.trollandtoad.com and www.starcitygames.com. Both sites offer booster boxes, and singles so you can order single cards that you may be looking for. I hope that helps.
Magic the Gathering has many formats, each with it's own list of legal cards. To see a complete list see here: http://www.wizards.com/Magic/Magazine/Article.aspx?x=judge/resources/banned
You are not restricted by what colors you have in your deck in any Magic format except for Commander (EDH). In Commander, you cannot have cards in your deck that have a color identity different from the general you chose. The color identity of a card is that card's color plus whatever mana symbols are in that cards text box (except for those in parentheses).
This question is unclear, but I'm assuming you're asking if you can resurrect a dead creature. The answer is yes; many spells in the game allow you to return a creature card from your graveyard to the battlefield. An example of such card is "Rise From the Grave".