Choosing strings for different tunings
You can use the chart below to work out what gauge of strings to use for different tunings. These strings each have a tension of just under 12kg/27lbs when tuned to the given note. For instance the optimum gauges for DADF#AD tuning would be .059-.040-.029-.022-.018-.014 instead of .056w-.042w-.032w-.024w-.017-.013 from the GHS true mediums that I put on, but the overall tension works out about the same. Try to keep the overall tension below 75kg/165lbs. Excess tension will suppress the dynamics and very excessive tension can cause damage.
If you want to switch between different tunings you will need to work out a compromise and experiment a bit, but keep an eye on the tensions.
Here is a string tension calculator that installs on your computer. D'Addario has an online calculator or you can use their tension chart. Flat wound strings are interesting on resonator guitars but I don't recommend them on mine as they are quite dull.
For the long scale guitars, lower the pitch by one semitone. (the G would be F#)