I don't have all your answers, but here is a start.
1) The driver information LCD panel to the left of the steering wheel is a Freightliner item supplied with the XC chassis package. Its of minimal value, shows some basic MPG, trip odometer, and engine temp info. If you have the Freightliner XC owners manual there is a basic description in there. At a rally years ago, a Freightliner rep giving a presentation passed out a "Instrumentation Operators Guide" document that had detailed instructions. I don't have a link to that 2005 specific version, but here is one similar http://www.rvtechlibrary.com/electro...mdc_owners.pdf
2) the power center above the entry/passenger consists of several different vendor supplied items. the primary part is the Intellitec 50amp Power management Center. My owners 3 ring binder (not the Fleetwood manual) had a separate manual from Intellitec describing this item. This panel is mostly automatic and simply shows whether you're plugged into a 50 amp or 30 amp supply (or running on gen) and if on 30 it shows any power shedding by device to stay under the limited amps. It also displays total amps being used. The only user input switch on this item is to manual switch to 20 amp limit, if plugged into a household type 20 amp supply circuit. This link is not the exact 2005 Fleetwood version, but something similar http://www.flemingsalesoem.com/intel...300684.200.pdf
The other items in this power panel are mostly on/off switches for various devices like HW Htr on electr. those are pretty self explanatory. The batt disconnect switches are only used when you want to disc all phantom loads from Batts, such as long term storage with no power supply. I've never disconnected my batt switches in 8 yrs since mine are always plugged in when stored.
Hope that helps, enjoy your D
PS: there is an active Discovery Owners Assoc and they have a Yahoo Group forum where many helpful folks answer questions.
PS 2: the original OEM version of that Freightliner LCD display was so hard to read that they eventually offered a replacement at reduced cost to existing owners.