You can't increase the limit of card drops currently. Foil cards are rare drops that will also count towards your card drop limit.

Most games don't allow you to get more drops, though a couple like Team Fortress 2 allow more after you have bought enough items in game.

Foil cards are randomly dropped, but rare.

i have a friend, his name is Google, hope he can help you -_-

Most games only drop half of the available cards. Which ones you get is random and there is a very rare chance it might be a foil card. You can only get the other half of the cards by trading or buying them.

I read in the official group that they planned on adding "Booster packs" for non-F2P games that would give an additional 3-5 cards. Not sure how they would be added, or if you have to pay for them (but I hope not...).

-> http://steamcommunity.com/tradingcards/faq <-

Upcoming changes posted by a Valve Employee

"Booster Packs: these will drop randomly for users who have received all their card drops from playing any given game, and who are continuing to participate in the community. Each booster pack will contain three cards for that game, and may potentially contain foils. The rate of drops will be based on how often cards are being used, to prevent too many flooding into the economy."

It says literally nothing about buying or paying for anything...