Hi and welcome to the site.
In answer to your questions:
1) Generally I haven't found mine to be thirsty on oil, just needed topping up a little bit between services.
2) No need to use 97RON. Not a bad idea every now and again, but they run fine on branded 95RON unleaded.
3) I haven't ever found a loss of performance when I have the air con on (although fuel consumption goes down a little). See what happens when you get the exhaust changed this week.
4) Again, somehting I've never had, but possibly down to the filter as you say?
5) The temperature gauge on mine always reaches the halfway mark within 5 minutes.
Any more questions give me a shout