Bad Boss Boogie
Also, if you're planning to have a boss in the factory level (I guess you'll do one because you said you're going to use Fear Factory), I recommend Boss Boogie because it reminds me a factory boss when I hear it.
I might actually do that if I find nothing else for the factory boss.
DK Island Swing (bit hard to find a good use)
There you answered your question.
Mine Cart Madness
I'm definitely trying to create real Minecart levels, better than those levels with the Minecart replacing the Rainbow Shell and the rails replacing lava. I'll probably have to use some tricks again. Chad already told me that there is a way to increase the speed of the SMB3 Platforms on lines, so that will probably be my first try.
And if I'll succeed, I'll use some of the DKCR or DKCTF minecart themes, because those are just better. Especially DKCTF has that one really awesome one, which is called Sawmill Thrill I believe.
Gangplang Galleon
Again, don't have space for a Pirate Ship level.
Bayou Boogie
I really love Bayou Boogie, but unfortunately I already made a Swamp level, using Forest of the Nopon (Night) from Xenoblade Chronicles, which in my opinion, fits a bit more than Bayou Boogie.
Forest Interlude
Way too overused.
Disco Train
Yeah, unless I get a spectacular level idea that would use this theme perfectly, I'm not going to use this.
Rockface Rumble
I liked that one, and I think it wasn't used that often, too. Just remember one level that used it. So I might use it for the mountain world, idk.
Boss Boogie
Will probably use this one. If it's the boss theme I'm currently thinking about, it's really cool.
From DKC3 I'll most like use the Underwater theme.
Homecoming Hijinx
One of my fav VGMs of all time, this is the one theme I'll guarantee you will appear in this.
Twilight Terror
Already used Stickerbush Symphony.
Seashore War from DKCTF will also appear in this, being my absolute favorite VGM of all time.