Many things will be similar to your GT such as floor pans and the suspension setup, give or take any components specific to the 3.2. The 147 does not have the same frameless doors as the GT so you don't get as many window gremlins. Squeaky upper suspension arms are just as common as are other bits like the rear hub bushes, handbrake cables and some other odds and ends. Older cars might require ARB bushes/lower suspension arms, I had to have mine replaced at 75k but many last into the 100k area, be sure to listen for any front end knocking.
1. Clutch/Dual-mass flywheel - There won't be much change from a grand if both these need replacing so always check the clutch pedal travel, if it's high then maybe the clutch needs replacing.
2. Swirl Flaps - Especially those fitted to the later diesel engines with the plastic intake manifold (see Autolusso - Swirl Flap Delete
for more) Many are trouble free but many also aren't.
3. Timing belt & water pump - The JTD engines have been known to suffer water pump seizure which can shred the timing belt and in many cases destroy the engine. They should both be replaced every 60k or 4 years whichever is sooner.
4. EGR - These are prone to sticking open and causing low down power issues as the valve allows the inlet to be flooded with exhaust gas. They can be reconditioned but many owners decide to blank them off and remap the ECU to permanently solve the issue. When you see the crud that comes off an EGR it's hard to believe that anyone thought it was a good idea to feed burnt diesel and carbon deposits directly into the inlet manifold, it really does stick like sh*t to a blanket.
5. Turbo Hoses - The OEM lower turbo hose in particular is prone to wear against the gearbox and eventually they blow, causing power loss and excess smoking. A cheap fix is to replace these with silicone hoses which do not expand like the original parts and last much longer. See - Alfa Romeo GT 147/ 156 Lower Turbo Hose - 1.9 JTD 16v 8v - Silicone - Autolusso New Alfa Romeo Parts
Hopefully this helps, there will be more but I'm sure our friends on here will point out any more areas for concern. Best of luck with your search.
147 Sport Q2: Autolusso Remap + Swirl Flap & EGR Delete, Mocal Oil Cooler Kit, JTD Performance FMIC Kit + High Flow Elbow, Wizard Downpipe, PF Pads + 5.1 Fluid, Autolusso Braided Brake Lines, MTech Short-Shifter, Autolusso Silicone Turbo-to-MAF Hose, Refurbed Q2's + Some to add later.