Re: appliance feed voltage control
Regarding the home made solar panels... Just keep an eye on them that they are producing current (with parallel connections, it is sometimes difficult to see when one panel drops output by 50% or more). Also, watch for burned areas around the cells/backing materials.
Regarding 12 volt appliances... Generally, most or are designed to operate around 12.0 to 14.2 volts or so (basically on a car's electrical system).
Most flooded cell batteries can use ~14.2-14.8 volts or so for "fast charging". You can dial the charge controller back to ~14.0 volts (for controllers with adjustable output settings)--But your deep cycle batteries will take much longer to recharge (possibly more time in the day vs hours of available sun).
And, you usually need to a deep cycle flooded cell battery to ~15.-15.5 volts around once every two months or so to "equalize" the state of charge (specific gravity) in each cell. Many "12 volt appliances" will check out at these voltage levels.
So, back to your setup... You have an accurate/calibrated volt meter than can read at least to 12.00 volts (and ideally, to 12.000 volts)?
Also, wiring can be a big issue with 12 volt appliances... Nobody things anything of putting a 120 watt load on a 18 awg extension cord at 120 VAC.... That is only 1 amp.
However, that same 120 volt load operated at 12 VDC is now 10 amps... You should have 14 AWG wiring, at least. And if those heavy loads are more than a handful of feet from the battery bank, it is not unusual to need 6-10awg wiring to carry 12 volt power any appreciable distances.
So--This is were I usually come back to. 1) Conservation. 2) Understand the load requirements. 3) design the system to support the loads.
Conservation) with any off-grid/solar system, power is expensive and not very much is available. It is cheaper to conserve a watt than to generate it. Using (efficient) LED lamps, limiting motors, using low power electronics, etc...
Load Requirements) Measure your loads. Use something like a DC Amp*Hour / Watt*Hour meter, a Kill-a-Watt meter for AC loads, and estimate the peak current/power requirements, etc.
3) Plan the system out... Generally, I like to design the system around the battery... Your load requirements define the battery size, voltage, capacity, type. And then the solar panels are deigned to keep the battery well charged and make up for power usage. At this point, you can also size the backup power (genset/charger) if needed.
At this point, you can also "play with the system"--Because of the problems you have stated ("12 volts" is really not "12 volts") and issues with expanding the system later (different battery bank voltage), sending power more than a few feet, etc... I really like to suggest that people look at a small/efficient AC inverter. It really reduces many of the issues with low voltage DC at a cost of ~15% extra power (conversion losses).
If you can live with 300 watts continuous (600 watt 10 minute surge)--I would suggest looking at the MorningStar 300 watt TSW 120 VAC / 12 VDC inverter. It has some really nice power saving features (inverters use a surprising amount of power with no or little amount of load).
If you, on occasion need a bunch more power (power saw, pump, etc.), you can always get a 1kW MSW inverter for not very much money.
In any case, the power losses from a DC to DC converter is not going to be terribly different than a good quality 12 VDC to 120 VAC inverter.
The Load Control on most charge controllers is only for ~8-10 amps and intended to turn off the power if the voltage falls below ~11 volts.
I believe I saw a couple Morning Star charge controllers that turn off if >15.0 volts or so... But it does not really address your issue (it is not a 12 volt regulator).
20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.