So, just to follow up on my original questions and to give you guys some closure (I know I hate when I read forum threads about people asking for advice, only to never know how it panned out), I thought I'd post what I ended up doing.
I ordered the Supercard DS One from Leetmod.com. Took them like 3 days to ship it. When they did, it got here in like 2 days. Pretty fast time in getting here, but I was starting to wonder if I wouldn't have been better off ordering from DealExtreme and saving like $15.
For the SDHC card, I ended up going with the 4 GB A Data Class 6 cards...bought 2 of those from Newegg. Price was like $14 apiece or so, and even though I didn't want to swap cards, I read far enough back in the posts in this forum to see that people were claiming slowdown with cards below Class 6, so I just went ahead and got the A Data.
So far, everything seems to work great. There was a new software update on the front page of GBATemp that I loaded right off the bat, and started playing. It plays everything I've thrown at it so far. Seems to save without issue. I love that the saves are just yet another file on the memory card...it'll make them easy to handle when backing up, etc. I love that I don't have to have special software installed to use the thing...since even the OS is just another file on the SDHC card, it's all just copy n' paste, and I can do it on any of my PCs/laptops.
I really have no issues so far, though I'm about to see if I can figure out how to load some emulators on my second SDHC card. Wish me luck!