Hi Glen, and welcome to the club.

All the GF models had Climate control as standard.. however, it is
more of a "manual" climate control, somewhere in between a fully
automatic system, and a standard heater..

Gear linkage... check underneath, and see if the heat shield is loose,
it can vibrate and make a right racket, also check the linkage to see
if it is catching on the exhaust pipe.. they run close together...
As for being "sloppy", then maybe the bushes are worn as you say..

The revs are supposed to go up when the A/C is on.. this is controlled
by the IAC valve in the throttle body, and is known to stick sometimes..
Check by having the car idling, and turn the steering wheel.. the revs
should rise.. also should go up very slightly with the lights and
heated rear screen etc.. if it doesn't go up at all, check the
electrical connector to the valve, or even use some carb cleaner.. but
as a last resort, you may have to dismantle the valve to clean it.

Also, 550 rpm is a bit slow.. it is suppose to be nearer 700, unless
they changed it from previous models..

As for the sucking noise.. I have no idea.. maybe a blocked breather
pipe or something... it could also be quite normal to an extent, as
there are vacuum chambers in the manifold..

Higher power models are usually down to compression ratios from
different pistons, higher lift cams, larger throttle bodies etc..
Again, I have no idea what they did to it.. but it is more likely that
they designed the original engine as the GSi, and detuned it for
economy and smoothness.
The Japanese models were more powerful, such as my old 2.5V6 KL
series.. they had a 200bhp KL-ZE, where all the other markets got a
detuned 165bhp KL-DE..

John