This sounds like a ton of fun. Out of curiosity, do you view this as an opportunity to try out 4e to decide whether to switch for future campaigns, or as a chance to have some fun while learning the new edition before launching a regular 4e game, or something different?
A couple of specific thoughts: The revised version of game 1 sounds fun, but it makes me wonder if game 3 (lvl. 5) isn't too much of the same too soon. Having two "defend the VIP" games in the first 3 sounds repetitive. Sure, they'll be different, but... I would suggest changing one of them.
It sounds like you're already planning this, but I would suggest keeping game 1 mobile. "Guard the goblin while he goes from A to B" offers more interest (terrain, ambushes, encounters with things that aren't part of the attack but are still a hassle, etc.) than "keep the goblin alive while they try to kill him."
For some of the mid-campaign games, in particular, you may want to give the PCs the option of choosing the next mission at the end of the previous one. I'm thinking mostly for games 4-6 or so. It could be as simple as the commandant saying, "so, do you have a feeling for which of these couple of missions your skills will be the best fit for?" As long as you're doing most of the prep work in the week or so in between games, which I assume you will be, it takes very little extra effort to offer three choices and then only design the one they picked, but it adds to the player agency. Otherwise, there is a risk that the campaign will last just long enough for the players to start feeling annoyed about macro level railroading.
Riffing on some of GiMiK1214's points, I agree that Yuan-ti seem like a great fit for that setting. If you would ever use them, now is probably the time (MM allowing, of course). Also, contra the concern about overusing the tieflings, I think it makes perfect sense in a game like this to have some recurrent foes. It helps give it more of a campaign feel, rather than disjointed games. And just because you're dealing with tiefling plots three games in a row doesn't mean that it's continuous hacking of tieflings. That can be part of one game, while the next is mostly the semi-undead hero (who could easily be something other than a tiefling) and the third is about a dungeon full of traps, monsters, and fiends, with some non-combat interactions with the tiefling warlord.
How did you pick the levels? You may want to revisit the precise selections once you have had a chance to read the PHB in more detail. Each new level should have a big cookie relative to the last, but you may want to vary it up from all of the levels being precisely where the biggest cookies arrive. Also, query whether you want 4-3-2 by tiers, leaving out the end of the last tier. You might be better off doing 3-3-3 and ending at the top of Epic (maybe even doing level 30 as the last game). That might be a progression like 1-4-7-11-15-19-23-27-30 (although I'm just pulling numbers out of thin air).
I wish I were going to be living near you when you run this so I could beg for a slot in the game.

Good luck with it!