it's sometimes a long way to make your own mod i think but if you really want just make firm yourself with the basics of file management. there are tons of tools to edit various types off game part engines. there's a helpful pdf document which can assist you understanding how ff7 is built, especially for core-editing:
q-gears.sourceforge.net/gears.pdfsome important tools for editing ff7 are:
LGP/unLGP (decodes the packed lgp files, eg. battle.lgp, char.lgp, magic.lgp,...)
Kimera (for models from field/battle/world .p .a .rsd .hrc , ... )
ProudClod (scene.bin)
Image2TEX (for .tex)
TouphScript (conversations editor flevel.lgp + world_us.lgp)
Cosmo (sounds, ...)
Zangan (Battle Scenes in battle.lgp)
HRC Resizer (change model sizes)
Timviewer (.tim images)
WallMarket (kernel.bin, kernel2.bin,scene.bin)
Palmer (flevel.lgp images conversion)
Aali's Driver (mod which enables most of this things)
as you can see there are different game parts to edit: models, textures, texts, sounds, music, stats, drivers, compatibilty with systems, language mods and most of these are actually available for editing.
there are manymany more tools. some are outdated, some don't run on newer OS correctly...
at least if you made a nice mod you can create an installer setup with NSIS.
You will find most information with the search function on qhimm or google.
it took a long while for me to find all mods to patch my game to the newest because i think there are more than ~100 different mods in circulation. a time saving project is the bootleg installer by PitBrat
http://forums.qhimm.com/index.php?topic=12008.0 you can see the magnitude of different projects