General plumbing questions

[cdat]

With the weather finally getting above freezing at nite, I can start too test my freshwater and black tank plumbing, I do have some questions regarding my setup.
On the passenger side, I have the ability to hook up to freshwater, either with a hookup directly into the freshwater tank, or a separate incoming water hook-up that feeds directly into the system, neither hook up is plumbing into a filter.
There is also a macerator pump on the the passenger side.
On the driver side, there is another plumbing bay, again with a direct line into the freshwater tank and a separate hookup that directly into the system. This side looks like the most jury rigged set-up I have ever seen, it appears they added a water softener and reran some of the plumbing lines with no real planning. In this case, the water filter is after the freshwater tank, after the water softener and little pressure tank, (cant remember the actual name), just before the water actually goes up into the house portion.
This side has a standard 3" dump valve and gray water bypass.
So, shouldn't the water filter do it's job before the water goes into the fresh water tank and thru the water softener, pressure tank etc?
Does Newell install a built in pressure regulator on the system, I have not been able to find one, not a major deal as I can add one on the incoming hose.
I plan on running a double water filter system, sediment and carbon, any thoughts from you folks on this.
I've never had a macerator pump on an rv before, am I better off running a hook up from the passenger side, over to the sewer hook up, or running the standard 3" and just using the macerator pump for when I go too a dump station?
I plan on redoing the plumbing system next winter, the entire system is 1/2 copper right now, would like to switch to pex when I rework the system.
Any thoughts or advice is appreciated.
john