Yeah they are safe. I used them recently since people recommended them on the forum here. Actually I was really impressed with the speed of processing. I ordered on Sat morning and they shipped it out on the same day, on a weekend. That was quick. I like them because they also use Google Checkout, which I prefer to PayPayl (they use that too).
I just read some post here that a guy from Ireland got his in 6 days which surprised him. So yeah i recommend them.
I can't answer question 2 since I didn't ask them to do it (don't have a DSi and I just install the firmware, AKAIO myself).
As for question 3, you should get it pretty fast. If that Ireland guy got in with 6 days, I'm sure you'd get yours quicker. I live in California so I got my in 2 days.