Indeed.
If you don't roll with the punches on your first playthrough you're a fool.
I am always deeply conflicted about this, as I personally grew to love the added challenge of not killing anyone, no alerts. When I first started playing MGS I typically just did whatever I wanted which typically switched from not playing very stealthy and switching between lethal and in the sequels, nonlethal.
When MGS3 came along I actually tried very hard on my first playthrough at the age of 14, and tried to be as stealthy as possible. A guilty pleasure of all MGS games for me is the tactile feel of each weapon, they feel different and serve different purposes, have different fire modes, and allow you to do different things.
I got Foxhound on my first playthrough of MGS4. If that's the right emblem I think. No alerts but I took my sweet fucking time so I didn't get the Big Boss emblem. I did a recent playthrough back around 2012 or so whenever they released that awesome patch that gave MGS4 trophies and allowed you to fully install the game so it doesn't have to stop to install the next chapter.
Man, I had like 96 alerts, and like 400 something kills. My subsequent playthroughs I ended up getting the Big Boss emblem, capturing the tschinoko, and finding every single Kerotan(with the help of the first edition Bradygames guides which weren't terribly helpful since most of the hardest ones are missing from the pages).
As for TPP, I don't know... I may just do kills allowed and stealth only.
Then go for ranks after I have had my fill of exploration and Motherbase/MGO.