You sound like you have thought about this a lot.
The newer flexible panels that glue to the top are getting pretty efficient. Layout to add as many as you can stuff on your roof. Even if you don't put them all up now, you can add more later. Figure out the maximum number you can put up there and get an MPPT controller that will handle that maximum. Use 8 gauge wire if you can, at least 10 gauge, and use a combiner box that you can add more lines two. Then you can add panels later as you want. You can also parallel new panels to your existing panels junction boxes instead of running them to the combiner box. You won't regret more panels. Install everything in parallel. Check each panel with a meter as you connect them.
Also look hard at your batteries. The whole six volt or 12 volt thing is pretty much irrelevant. Pound for Pound, it pretty much works out the same. Again, stuff as much battery as you can into your system. The key is not whether it is 6 or 12 volts, but rather your final amperage capacity in 12 volts. Personally, I have 4 LS-16s, which are 6 volt, with 2 pairs in series and those pairs in parallel, but that's just what worked best for me.
If you add a good voltage and current sensing meter, it will let you know your usage and the state of charge. Its easiest to estimate your state of charge using your voltage, but this changes with the load, so you need to know that as well. There are several good systems available for this.
2005 Coachmen Sportscoach Encore 380DS
2014 Jeep Wrangler Rubicon Unlimited