I'll add a step between 2 & 3 - pick a color that was offered on another Alfa model, same year. The Zagatos and Montreals (starting 1970 I believe) came in some amazing colors. I would be shocked if you couldn't find something that piques your interest in the entire Alfa catalog. I've been told that the factory would often grant such cross-model paint requests, so strictly speaking this isn't going too far afield.
As a minor color snob and avid classic car window shopper (and actual shopper) I can volunteer that for me a well done bare metal inside and out respray in a factory color using good paint would detract zero dollars from the car's value - presuming I like the color. Most would agree that going from something interesting and unique like Giallo Ochre to plain old alfa red would incur a penalty, but I think even more people would agree that having rock solid paint sitting on a documented, straight rust free car trumps nearly everything. These are old cars after all and even the "survivors" have rust, so body condition and the quality of paint is an enormously high priority. After that, these are cheap cars. A motor can be rebuilt and hopped up for a few grand, all the suspension pieces are cheaper than honda parts, ditto brakes, etc etc.
Finding pictures of cars in colors you like is a full time job (see my recent post looking for decent Bluette pics). If you name some of those you're interested in I can post some of those I've collected over the years. Do you like unique/period colors? Bright colors? Blues, reds, greens? You can also surf the "lets post pics of 105's" thread or this group on Flickr: