If you want to be ambitious, try messing with effects with the ever-so-free Audacity and fuse the two voice files into a single one. Especially if one (or both?) of the voices echo epically. :3 Though the 1 frame later option works just as well if you just want to have one follow the other.
O_O* Lets see. lol
Audacity seems to be the universal choice for free recording software. Most of PT's vocal members uses Audacity. Also, most ears can't tell the difference with WAV and MP3. WAV makes people feel more comfortable with the quality, but takes up 3x the space, so I always go with MP3. The voice actors who give me WAV, I just convert to MP3 in favor of space and flexibility.
Inserting a voice for battle is done the same way as an event on the map...text wise that is.
Game/Database/Troops/Select x Troop(s)/Event Box/Play SE/Insert Text/Stop SE
^ Open up your game, go to the database icon, go to the troops tab, and select the enemy you want to have speak (or your character speak to the enemy). There will be an event box for you to enter the sounds/songs/tracks/weather/ect for you there. That's where you put the voices in for event conversations.
As for the battle voices, I believe there are two ways for you to do that, but before I give you the recommended way, I want to try and make sure it works first. It involves Random variables, condition branches, and common events. So try not to take my word for this section. If you want to do the exact thing I did, just place a SE (ie, the voice) into the animation tab to that corresponding move.
And finally, to find solid good voice actors, you'll need to have a smooth tongue like I do with the drama class ladies in your school. :3 That, or, well, go to www.voiceactingalliance.com to find some solid voice actors. Whichever is easier for you.
Hope that helped. @_@