To get more informed answer you need to provide more information. How much roughly are you looking to borrow? What term will it be repaid over? Will you be charged interest?
Technically you could borrow a large amount of money without any tax being payable provided there was no interest charged.
In my view, €600,000, but some would contend an unlimited amount.
The taxable value of a loan for CAT purposes is linked to call deposit rates; I would use a rate of 0.5% to be prudent (i.e. €600,000 x 0.5%) but in reality 0% is probably just as reasonable.
The €3,000 limit relates to gifts and a loan is not a gift.