1. your thermostat is almost certainly cream crackered. just check to make sure that the fan is not coming on, as it could be that the temp sender is faulty. there are two sensor heads in the same sensor unit so the gauge has seperate sensor. I would also run your hand down the back of the rad when tis cold to see if its soft and crumbly. usually if the stat goes the rad is gone as well, the two cover each other up. rads only last about 5 or 6 years.
2. tyre wear on one edge is typically due to tracking and not the common mistake of camber. camber is not adjustable anyway so don't worry about that but tracking is. sounds to me like both your wheels are pointing outwards of the vehicle. suspension arms are a niggle point on the 156 but i doubt in your case. bottom arms will rumble as you go over bumps and if you look in the bushes you will see them physically worn out like the rubber is missing, should be filled up outside. top arms will squeak if them are worn or dry - usually a good grease will help the top arms out. if you can feel and hear a knocking in your feet your anti roll bar needs attention, but its less common.
3. get your tracking checked first but I would also consider the wheel balance. chances are however given the tyre wear issue you are facing this should be your first port of call - tracking. a check for me costs about £40 on a top notch laser system locally, £50 for check and adjust.
4. by the sound of the probs you are having you may need some new tyres before the MOT - remember th change in axle pairs to keep the car's grip levels balanced, it is that important!
1999 156 1.8TS Sport Pack 3
2001 166 3.0 V6 24V Super
2003 156 GTA 3.2 V6 24V
2005 156 1.9 JTDM-Jet Sport
2008 159 1.9 JTDM Lusso
1997 GTV 2.0TS Lusso
2001 147 1.6TS Lusso