I haven't used a Hex Editor in a long time, but I'll try to answer your questions.
1. In hex, values are normally set in pairs (for example, FF FF, or 54 A7), so he added a 0 in to keep it that way (I assume it is 0B B8)
2. You're using the correct file, don't worry (unless there's another file in there that looks interesting, keep me posted)
3. It basically means the things the hex shows (if you know what 'yields' means, you'll know what 'hex yields' means)
4. You can find some of those in the Tutorials section, or from Google (too lazy to give links, sorry). From experience, finding coin/gem values is pretty simple (simply write down your value of coins, and then convert from decimal to hex, and then search).
That's what I have to offer. Sorry if my information is wrong/misleading as I have not hacked in a while.