Welcome to the Forum. It’s very wise to have the belt(s) changes at that mileage.
The price in Denmark would be around € 500,- incl. VAT. Have the tension pulley(s) as well. If they are black (early, chap, type) change it (them), if white and not worn, it’s all right. If the engine sounds like a diesel the variator is gone. If the noise is bad, change it, if not, it worth considering, as the belt(s) has to be changes every time they are taken off. When I bought my 2,0 16v the variator had done less than 18k miles and clattered a little, especially when the engine was started hot. The dealer who’d supplied it then new and serviced it since, said not to worry, it might get worse but it’ll not break. I then had the belts and pulleys changes (€300,- at an Alfa Specialist). I’ve just sold the car, then the variator had approx. 48k m behind it, the noise still bearable.
You write that you consider chipping. If HP is important, I’ll consider a 2,0 16v instead. You’ll get the same 10-15 % improvement of both HP and torque so it’s worth having the extra punch from the outset. As your considering alloy wheels, as well; why not find a 2,0 16v “S” which comes with 16” dark gray or black Speedlines, lowered suspension and Recardo seats among other goodies.
I’ve booked flights to Dublin in August, so, please, all Irish pray for some sunshine – your beautiful green island looks it best in the sunshine. Unfortunately, I couldn’t find any car rental companies offering Alfas, so the holydays are half spoiled (just joking). Maybe I’ll meet some of you (in a pub)
Good luck finding the right 155.