For all the reputation that US immigration officers seem to have around the world, keep in mind that they have 30-60 seconds to profile you as they look over your entry card. On their end, the questions pretty much come down to:

1. Is this person a risk to commit a crime?

The two red flags here these days are entry from certain Central and South American countries (illegal drug concerns) or if you've got an Islamic-sounding name. If neither of these apply, the vast majority of the time you get parsed as 'low risk'

2. Is this person a risk of overstay?

While I generally agree with not saying more than needed, phrasing it as:

"I'm here on a two week holiday from work to visit friends'

or

"I'm here on two week holiday from university classes to visit friends'

is a reminder that you intended to fly the return leg of your ticket because you've got something to go back to.

3. Is this person planning on working while they're here for alleged tourism purposes?

Two weeks is a normal holiday time frame for our European guests. It's also not really enough time to do work illegally outside of Visa Waiver/tourist visa. There is far more concern about illegal work and sufficient funds if your return ticket is 10-12 weeks out of arrival.

As for staying with friends- perfectly normal. My parents have even found themselves offering to put up kids of German friends for free so they could extend a trip to the USA for a week and sty on budget.

As for credit cards- so very easy to get over here (plenty of stories about a pet cat or dog being given a credit card with a $10K limit) and the assumption is that if someone has one, they've got sufficient credit limit to cover what cash does not.

I'd actually recommend not carrying too much cash across a border- large amounts can be a sign of illegal activity like drug payments, and the exchange rate you get an an ATM upon arrival is pretty much the same to somewhat better than what you'd get arranging for US Dollars from your home bank before you leave.