I can try and answer your first question.
I highly suggest Advance Text for editing text, if it is compatible with your computer. Here's how I do it...
-Open up Advance Text.
-Load the Pokemon Sapphire Rom.
-Select "Search". This is where you enter a keyword or a phrase. For example, if you enter "POKéMON", Advance Text will search all text in the Rom for anything that contains "POKéMON". If you check the box underneath the search windows, the results of the search will contain the entire dialogue message. Otherwise, the results will show the dialogue message beginning from the word you searched.
-If you want to see more results containing the keyword(s), click the "Resume" button.
-Once you've found the text you want to edit, click the "Write to INI" button. A window will come up asking you to enter a section name and a text name. The section name is sort of like a folder, while the text name is like a file. Suppose you were editing a bunch of messages displayed on signs. You might want to call the section name "signs" and the text name something like "sign1". If you decide to search for more text messages from signs, you can save all these text messages into the "signs" section name.
-After you've done this, click "Write to INI".
-You can then close down the Search screen if you don't want to search for any more stuff at the moment. Out in the main Advance Text program, there are 2 large windows. The window on the left has all the section names. If you select one of these, you can see what text messages are saved in that section. Click one of those text messages to have it appear in the window on the right. Then you can edit it all you want. Try to keep it the same length of characters as it originally was. It can be shorter if you want, but things get kind of difficult if it's longer.
-When you've finished editing, click the "Save Text" button to save the text to the Rom. It's possible to save text messages that are longer than the original messages, but it has to re-point the text. This usually works, but I've had it fail once for me before when attempting to repoint. :(
Oh... one more thing. If you're typing text in the text-editing window and you don't press Enter to start new lines, it's going to come out a big mess when you play the Rom. What I do is press Enter to start a new line when the text gets about 2/3 to 3/4 of the way across the text-editing window. That'll bring the text onto a new line in the Rom. It has to fit within the dialogue boxes in the actual game.
There is also a way to edit text using a Hex Editor... but I know nothing about Hex Editors, sadly. :(
Also, about that question I asked earlier about PET... you may disregard it. I had to manipulate the trainer's team a lot, and add and subtract Pokemon occasionally, but I eventually got Brendan to have the team I wanted. :)