Actually, once you finish a main story, you can then play Shade Impulse Story, and when you finish that, you'll unlock the Duel Colosseum, then you can start farming ;) I have over 1M gil so far, you'll start farming way too fast once you get the DC.
Dissidia can make for some epic fights. Most of my fights tend to last at most 20 seconds, due to me wanting to finish them as fast as I can to build up a nice chain on Blackjack, but some fights against Level 130 have taken me over 5 minutes, with counter, counterblocks, and one minute long dodges xD.
Current PC Build
CPU - i7 8700K 3.7 GHz (4.7 GHz turbo) 6 cores OC'd to 5.2 GHz with Watercooling (Hydro Series H110i) | MB - Gigabyte Z370 HD3P ATX | Gigabyte GTX 1080ti Gaming OC BLACK 11G (1657 MHz Boost Core / 11010 MHz Memory) | RAM - Corsair DIMM 32GB DDR4, 2400 MHz | PSU - Corsair CX650M (80+ Bronze) 650W | Audio - Asus Essence STX II 7.1 | Monitor - Samsung U28E590D 4K UHD, Freesync, 1 ms, 60 Hz, 28"
