You can give the player Battle Points by using the following commands in XSE:
setvar 0x8004 0xYY // Where 0xYY is the number of Battle Points you wish to give
I am trying to use the warp command in one of my scripts and it just takes me to a black screen. What can I do to fix that?
In addition to what jsziede said above, ensure that the map you're warping to isn't corrupted. Try walking through a regular door warp on the overworld in addition to warping through scripting. If you still wind up with a black screen then the chances are that your map's data has been corrupted somewhere along the way. You will have to reinsert the map or repoint any misdirected footers if this is the case.
In terms of what game is the best to hack, that's a pretty subjective question. However, just about anybody will tell you that Fire Red has the most compatibility with tools. If that's all you're looking for then go for FR, but don't let accessibility be the only deciding factor when deciding which ROM to hack.