Hi Panos and wellcome. I think that you shall ask at
AlfaOwner.com
This site is mostly for US models and owners. Alfaowner.com is based in England and is visited by Alfisti from all over the world, but especially Europe. From 1994 no Alfas have been officially been imported to the US.
But some quick answers.
1. Yes, but very much have to be modified, I douth anybody have tried.
2. Repair it or the gear linkages (rods from gear lever to gear box.
3. Their might be Turbo kits for you model, but where and how, I don't know. Supercharger kits, I dought it.
Kits are best, you gets all the parts you need and it's been tried before and probably works. Putting parts from various venders together will never be optinal, and may even harm your engine.
Before you start, you need to make sure your engine is up to the extra strain that at Turbo/charger will put on it. It might need a rebuild, and probably new low compression pistons if you want more than 20% more power.
Erik