I'm not expert but two of the jobs above there are biggies...imo.
The heater matrix is a right pain. I did this on a 1995 non-Alfa car 4/5 years ago.. ouch, painful. But it is satisfying when you complete it...
Full body respray, we had one done on a non-Alfa classic (restoration) 2 years ago and it was just south of 6k euro. It was a superb job but we though we might have gotten away with 3 or 4 grand, but no....some panels needed a second, fill, sand and spray etc. That was the cost for the bodyshop to sand, prime, spray and cure just a bare metal shell... we did all the stripping etc.
Sometimes then a job or a part will cost double what you expected, so some other part does not get replaced with a new one, just a reconditioned etc..
To be honest any money you put into a loved car will not be realised at the other end of the job... it's negative equity! The problem, imo, is when to stop replacing and spending. But if you love a particular car and have a sentimental (non logical) attachment to it then the enjoyment you get is priceless.... that's my take on it anyway.
If you do decide to spend, it's a bit of a commitment, but when your car is perfect you will keep it for the long-haul, and, you'll be glad you did what you did.
Best of luck........ BUT! if you're in a serious relationship at present then do get the buy-in from your partner. Because if you go ahead on the spend/refurb there will be 3 of ye in the relationship then... believe me.