For (1), look at the mass guild mailing addons. They've had to throttle down to prevent the user being kicked. I don't know what the timing is, however.
3) It varies wildly. Sometimes it only takes a dozen seconds. More often you'll have to zone (or even relog) in order for the mail to show up.
4) The mailbox can be full. It might indicate that, but not sure.
5)
http://wiki.esoui.com/API and search for "ResearchLine"
6) The most common way to get binary into text would be base-64 encoding, which is essentially A-Z, a-z, and 0-9 then 2 extra. If you counted all special characters you could probably get more, but it'd be more difficult processing, as it isn't a power of 2.
Base64 puts you at 64^2, which is 4096 distinct values (128 bits). For crafting, you're looking at 14*9=126 bits for clothing alone, which would need just 4 characters if you bit pack (0 or 1 for if learned). Since woodworking has roughly half the items, you could store all 3 hard crafts in 10 characters. (Note that this doesn't leave room for future traits. You could just add characters onto the end for that when they appear, though)
Linear Mode
