1. Clutches will bite high if worn although it is difficult to say how long each will last. Some are good for 100k+ and others not so much. Mine was changed at 65k along with the dual mass flywheel which cost the seller £900 so it would be nice if this repair has been carried out already.
2. The timing belt should be replaced every 50k or 4 years in addition to the water pump. This seems to be the JTD's only real weak point as most timing belt failures tend to be caused by a seized water pump. £350 is a good price for a timing belt/water pump replacement. Check the oil too, I change mine every 4-5k so check for signs of neglect and if it's low I'd look for a better example. There are still plenty of decent examples around for that kind of money.
3. Upper wishbones can creak and moan when worn, drive over a speed bump (slowly of course) and listen for knocks and rattles. Budget £80-£100 per side including fitting for this. Lower wishbones should last longer but listen for any knocks from the front. It might be the ARB bushes or the drop-links, the latter being a cheap repair, around £15 per side. Replacing the ARB or its bushes is a little more involved.
4. The bodywork picks up knocks easily due to the design and the metal being a tad thin. Check panel gaps for collision damage and overspray and the sills for damage from using incorrect jacking points.
5. There was a recall some years ago for faulty bonnet catch mechanisms, which in some cases caused the bonnet to open while driving. Check your local dealership for info and if necessary a replacement catch. (Ta rockhopper, the catches weren't replaced, just cleaned.)
6. As with many diesel engines, the JTD/JTDm has an EGR valve which over time gets gunked up and occasionally sticks open causing a loss of low down power, or even stalling. The EGR can be taken off and cleaned up but usually requires replacement soon after it's seized. Regular maintenance can help prevent this issue, see the guide here on the forum.
7. Electronics should be sound but check everything works as faults can be difficult to diagnose. Also, have a play with the air-con/climate control ensuring you have a full range of temperatures.
8. Check the tyres for uneven wear as this may clue you in to suspension issues or poor alignment. The 147 does like to chew up the inner edges of its front tyres but a quality alignment can help reduce this.
9. Rust shouldn't be an issue but it won't hurt to check, the floor pans in particular are known to rust on early 156's on which the 147 is based. Exhaust back boxes rust badly but are robust, if this bugs you, you can get replacements for around £50 or check some of the aftermarket solutions.
Check these also:
Alfa Romeo 147 Buyer's Guide
Best of luck with your purchase. It looks a nice motor.
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.