I would just get some 0 or 00 and run the cable to the front battery, with one size larger grounded back to the battery. If I had an isolated deep cycle aux battery, I would still power the winch from the starting battery. The winch likes the CCA. If you winch a lot get two decent batteries with the cold cranking amps in mind. Winches like juice, and the startup bump can be a heavy amp load. It's why you want your cutoff to be something with a working rating of say 300 amps but a surge rating or 1000+. If I have a cutoff, I like it near the winch clutch. I've never used a deep cycle for a winch, and I've never isolated the winching battery from my starting battery. But there's lots of opinions on that for sure. I just like simple, because it's simpler!
j