Thanks for your post.
In general, Solar would not need a fuse unless you are wiring in a big array. This is generally only caravan/RV type installs so shouldn't be a problem in a 4WD type setup. If you do want to put one in however, no issue there. Just ensure it has enough overhead to handle any spikes from the output (EG use a 20A fuse for a 10A output panel).
No VSR required with these units, all the switching is done internally and will cut in/out as needed. The older BCDC1225 and BCDC1240 units did have a change-over relay previously, but the current model 'D' range do not need this.
And yes, it is 6 B&S cable coming out of the unit. You will definitely need this, or thicker depending on your length in cable run.
I trust this has answered your question in full. If you are still requiring assistance, please call us on REDARC Tech Support on 08 8322 4848.