Let out the clutch until you attain the speed you want then put the shifter knob into the "neutral zone" (Trek reference) and let off the clutch entirely.
Coast...
People of the age you're referring to have learned some things through life and maybe you/he should heed their advice (especially since he asked for it).
Or was the goal simply to hopefully find justification to do what he already knew to be a bad idea?
Not really. I have a 2013 370Z with the high end system (Bose). I test-drove a 2015 GT Premium with the upgraded stereo and wasn't impressed. The one in my Z is far better.
I think this sounds like a very bad idea. You already have a relatively new car and don't make much money. Think about what those payments will be taking from your monthly income - if/when you're paying your own insurance you won't even have money left for gas, much less eating out or doing...
You do make good money; don't let these outliers get you down. The median HOUSEHOLD income in the USA is about 51k and that's with most being two earners.
That's household income. An individual making over about 195k is in the top 1% of all earners.
http://www.whatsmypercent.com
Put in 195,000 and hit submit
Your percentile is: 99%