You can obtain the ventures (currency) from GC by exchanging GC seals (1000 seals = 5 ventures), from beast tribe quest (at higher levels already 10 per each, could be more at highest one, I've not reach that yet) plus as rewards from leves. So while it's somehow "Limited" how much you can gain (by fixed daily alotments for tribe and leve quest) if you want to go crazy you can produce as much GC seals as needed by running FATEs so in theory you should never run out of ventures even if you'll be using it every hour on quick explorations for both retainers.