Yes I am aware that using an SRPG in Japanese for a first romhacking attempt ever is a pretty dumb idea. But stay with me anyway. As mentioned in the topic, I'm trying to hack Super Robot Wars Advance for the GBA and I'm having a bit of problems understanding how to do things...

I pursued some of the FAQs in the "Getting Started" section and decided to work on trying to change some of the script, so first I got to make a table. I'm using WindHex for this and I'm not sure if there's any program better because the lack of undo function really annoys me. If there's something else I'm supposed to be using, please let me know.

One of the FAQs recommended naming your character something, then backing up the save game and naming him the opposite (I chose "AIUEO"), then comparing the two files and look for that. I managed to find and build a table with those values, and it does in fact give me her name (and the rival's name) but for some reason, no one else has their names in the file.

Is there some other way I'm supposed to try to get character values to build a table? I've read about relative searching but I'm not sure about how I'm supposed to use it with WindHex, it doesn't seem to accept Japanese characters for the relative search value...

Secondly, I decided to move on and try to edit mecha stats or game statistical data in general, I thought it would be easy, there's a list of numerical data up on GameFAQs and all I have to do is find the numbers using a search right?

I searched for Vysaga's HP of 4100 which gave me 1004 for a Hex value when I inserted it in a calculator. Suspiciously the Hex search only gives me one result, and changing it does nothing. Is there a problem with my calculations?

Also I'm curious, but how do people find offsets for things like sprite data with no obvious numerical connection? Other than trial and error, is there a better method to go about doing it?

Well, that's all for now I guess, I hope someone can help me here.

SRW A probably uses the Shift-JIS encoding, just like the other GBA SRWs. The dialogue text is compressed, though. I don't know about the normal menu text and names, but they could also be compressed.
The game can save data in any way the developers like. Did you search for the little endian (lower bytes first, so 04 10) value? Did you start a new game afterwards? Otherwise, it may not be as easy to change.
Bear in mind that VBA saves are sort of byteswapped (every 8 bytes are stored in reverse order, so insted of 12345678 12345678, it's 87654321 87654321). Non-variable names usually aren't stored in the save data.
 
Sure, there is a much better way to find such things. People use a debugger for such things, and trace the data back to their origin. Doing so may require rather extensive assembly knowledge, though, so it's not really suited for beginners.

For compression, IIRC there are several good documents about it in our Documents archive.