Human Revolution is a prequel to the first Deus Ex so you won't miss out on any preceding storyline by playing HR first. However, HR is built on the same concepts (sneaking, finding alternate routes, talking your way out of problems) as the original and you might feel a little behind the curve since you're picking up the game concepts for the first time. And yes, you may miss some inside jokes about crawling around in ventilation ducts (it happens a lot in the first game, and a lot in HR as well).
Although I haven't finished HR yet, I expect it will tie into the events of Deus Ex (already there are some references to the future of nano-augmentation, a heavy plot point in the original) but you shouldn't miss out on these things, they'll just make sense when you play the original later on.
As for Invisible War, it takes place even later after the events of the original so you won't be missing out on any plot points there. In all honesty, some people don't really consider IW to be a proper sequel as it dropped or reduced a number of features that many people enjoyed from the original (most of which are back in HR). So don't feel bad if you don't play it, ever.
The "Missing Link" DLC has been announced (for October), but this will apparently be set in the time between Jenson leaving Hengsha and arriving in Singapore so will not carry the story forward past the end of the game, but it may well provide more exposition on how the games are linked.
However, they have already made some fairly strong links between DE:HR and the original. Specifically, the little hidden element from the credits (that you mention) infers that Megan Reed is working with the Bob Page (and therefore the Illuminati), so is presumably using Adam's DNA to help them develop the nano-augmentations that appear in Deus Ex and the "nanite-virus chimera" mentioned may presumably result in the Grey Death.
There are also other weaker links throughout the game, for example when Jenson detonates the bomb in Hengsha shipyard he inadvertently allows Tracer Tong (a major character in Deus Ex) to escape the island. There are others too, I'm sure, but I won't try to list them all here.
A few of the Wikia pages provide more in-depth information, here's a few that are the most pertinent:
Deus Ex: Human Revolution, Plot
Adam Jenson, 2027
JC Denton, Early Life
Nano-augmentation, The beginnings
Best Answer
I knew there was a shop in the first city hub that sold them, but a quick check on the wikia page gives a fuller breakdown:
This doesn't seem like many, but they can only be used on the 10mm Pistol, Combat Rifle and Machine Pistol anyway.