Sounds like some lofty, yet fun goals, Matt! Vintage MOC is so much fun.
Putting on my non-Stormtrooper-centric thinking cap, I'd say that you shouldn't have much trouble finding the first 21. However, finding them in unpunched, unstickered condition will run you a little higher monetarily. If you're looking for specific cardbacks only, that's where you might run into trouble. Some of the 21 backs (both SW and ESB) are mighty rare (especially that dang Stormtrooper!
I wouldn't be concerned about what other people think of your collection. As long as you like it, that's all that matters. In fact I don't recall ever hearing or reading someone criticizing someone else's collection for being mixed punched/unpunched, stickered, mixed conditions, only C-3s, etc. (unless, of course, they were just trying to be a jerk). I mix and match condition, punched/unpunched, price stickers, and offers (of course). I mainly just concentrate on the condition of the figure and bubble and the overall presentation of the card. I have some pretty crappy cards, too, but they were the only examples of that particular cardback that I had come across, so it wasn't a big deal.
As for the ugly punches, I know what you're talking about. However, I don't know of any general rule as to what time period the ugly punches were found. I have them throughout my collection. But if you're going for unpunched, this is kind of a moot point, now.
If you're a little impatient about getting all 21, you might want to do what I hear other collectors sometimes doing. They buy the figures/card that they want regardless of condition. They then continuously search for better condition examples to upgrade and sell off the lower grades. This way, they always have a complete collection, but are still engaged in "the search." This might be easier on the wallet, but when has collecting ever been "easy on the wallet?"
If you haven't done so, I would also suggest getting a copy of John Kellerman's book
. It lists just about every single cardback/figure from the vintage line and a bunch of other stuff. Definitely a must for a collector of vintage MOC.
Again, sounds like some fun ahead for you!