その企業は___な資金を背景に、大胆な投資を行った。

潤沢 (juntaku) means abundant and ample, often used for funds or resources with a nuance of surplus. 豊富 (hōfu) means simply plentiful. 多額 (tagaku) and 莫大 (bakudai) refer to a large amount of money, but lack the nuance of 'surplus' that 潤沢 carries.