First of all, most credit card issuers that will approve you for a credit card will reduce your credit limit upon your request. It is far easier to get them to reduce your credit limit than to raise it!
Second, shopping on the internet has never been safer than it is today. This is especially true,if you limit your shopping to merchants that you know and can trust, such as Amazon, Best Buy, Wal-Mart, and others. But, you also have an option to create a short-life virtual credit card number that is temporarily linked to your credit card account. This service is offered only to customers of Citibank or Bank of America. So, if for some reason you have any doubts and are not comfortable giving away your credit card number virtual numbers will do the job!
And finally, on immediate use of a credit card, after an application was approved – there are credit card issuers that allow such instances. For example American Express, sometimes, provides a virtual credit card number that can be used for online shopping immediately after an online application was approved. However, AmEx does not disclose its policy on providing such perks. The only sure option left is to call your new credit card company and request to overnight the new credit card, which may come at an extra cost.