You should be able to get it for around £3.5k, that's what I paid for the one I bought a month ago in what sounds like very similar condition.
My clutch is on it's last legs and the cambelt is pending a replacement (worth checking when/if it has been done on your intended purchase). You may well find the suspension is on it's way out, I'm fairly sure the rear shocks are past their best on mine. Other than that I couldn't find anything amiss bar the rear windows not going back up if lowered.
Recent replacements include brakes all round and the exhaust, so worth checking those, looks like they chew through front pads at an astronomical rate.
Compared to a 106GTi it will feel big, tall, and wallowy. At normal driving pace the suspension feels at least as firm, but if you push on the extra weight causes the suspension to compress and the whole car to skip across the road. Initial turn in is very sharp, possibly more so than a 106, but the steering lock is rubbish. Weighting wise the steering is a good bit lighter and missing in a chunk of feedback, certainly nothing like as fun to throw around. Having said that it's not bad for a heavy lump, much better than a 206GTi, and does resist understeer well.
Mine came on top quality
Federal tyres which make for an interesting drive. Loads of tyre screech on 60-70mph bends, and comically lacking in outright grip. Feels suspsiciously like it dances off the bump-stops should it encounter a compression mid-corner, something that you certainly wont be used to.
Performance wise: once rolling it is not far off the pace of a 106 with a passenger, as you know extra weight in them hinders performance fairly impressively. With just a driver in each the pug is a reasonable amount quicker.
Ergonomically you will be right at home with the brake and accelerator being neigh on touching. After that the Alfa is a nicer place to be, for a normal drive (once you lower the seat as far as it will go). One problem I've found is the (on, midway, off) 3 point accelerator pedal, which causes lots of ankle pain should you be driving around sedately (such as cruising on motorways) really wish it had cruise control. Gearbox should be nice and precise, the throw is a bit long, but otherwise very good. One thing to be aware of is the rear seat does not fold down, which is a royal pain.
MPG should be 10-15 up on what you are used to - low thirties becomes mid forties.