A 150 is a big, expensive tank to drill your first hole on.
Drilling isn't difficult. You can get the diamond holesaws on that famous site where you bid on stuff. I paid about $25 for a 1.75" bit (for a 1" bulkhead) and have drilled many holes with it. The slower you go and the more water cooling you use, the longer your bit will last.
Usually if you get it from famous site where you bid on stuff seller who sells them specifically for aquarium hobbyists, they will include an instruction sheet that shows you how to do it.
Back to my original point though.. it'll be a real expensive shame if your first hole doesn't go so well on a 150. You can buy a hunk of glass to practice on.
Usually, tanks that big have tempered bottoms, and cannot be drilled. The sides are usually regular glass, but you need to confirm that with the manufacturer.