i go to the scrapyards almost every week, its criminal how many great bits are just sitting there in the mud rusting away. but ti means bargains for anyone who can be bothered to go and get them.
i've done the pas conversion on an old rover 200, it only required the pump to be fitted along with its hoses and the steering column with the rotarty valve on. just 2 hoses to connect them together. to power the pump you need to get a belt and make sure your engine has the required pulley to drive the pump. usually the pump will be driven by a pulley which is present on all models and the only difference is the belt, however some models have an additional pulley only on pas models so check out how the pump is driven on a punto with pas.
electric windows is very easy. you dont need to worry about wiring it in the same way fiat did. you will need the elec window motors, the switches and thats it if you're willing to wire things up in your own way. if you source an ignition live and earth to each switch and then wire each switch to its elec window motor it will work. i suggest you fuse the live to eahc switch. also to get the switches illuminated they will have another pair of wires, just connect in parrallel to the illumination wires on another switch. its easy.
central locking can be more of a pain to get right if removing from a donor car. its often easier to buy a universal kit with a pair of actuators to fit in the doors. then you will have remote central locking as most diy kits come with remotes. i se them on ebay for cheap all the time. (less than £20)