Well, I think you did it fare more complex than necessary 
For example, take a look at the Mode. You are using five items, where you only need one item.
Number airconMODE "Mode is [MAP(airconmode.map):%s]"
The mapping file ./transform/airconmode.map :
1=Cool
2=Heat
3=Vent
4=Dry
5=Auto
-=-
NULL=-
and ONE Rule:
rule "Aircon Mode"
when
Item airconMODE received command
then
var String body
switch (receivedCommand) {
case 1: body = "{\"SystemMODE\":\"cool\"}"
case 2: body = "{\"SystemMODE\":\"heat\"}"
case 3: body = "{\"SystemMODE\":\"vent\"}"
case 4: body = "{\"SystemMODE\":\"dry\"}"
case 5: body = "{\"SystemMODE\":\"auto\"}"
default: {
logError("airconmode","Wrong Mode! {}",receivedCommand)
return;
}
}
sendHttpPostRequest("http://192.168.0.253/SystemMODE", "application/json", body)
end
In a Sitemap, you can chose to either use it as a Switch with multiple buttons:
String item=airconMODE mappings=[1="Cool",2="Heat",3="Vent"]
String item=airconMODE mappings=[4="Dry",5="Auto"]
Please take account to the fact, that I used 2 lines as there are 5 Buttons, which maybe will be to wide for some UIs, but as you can see, this is no problem at all, and this is 2 Lines vs. 5 Lines 
But there is another option:
Selection item=airconMODE mappings=[1="Cool",2="Heat",3="Vent",4="Dry",5="Auto"]
This time all options in one Line, as this will draw a drop-down-selection.
Same is for Fan
As you are already polling the System settings, I would rebuild the polling rule to set also the other items (a bunch of lines per Number item for Mode and Fan.
In question of zones, I would consider to use Grouping and only use one rule which fits all.