Will Google analytics track if instead of using the 3 mandatory variables (source,medium,campaign) I use just source?

It's isn't just you. Adobe reported that "over $21.8 billion in global ad revenues have been blocked/lost so far in 2015." largely thanks to mass adoption with the AdBlocking software :) 21 million users in 2009, to 198 million active global users as of June 2014-likely overtaking the other comps entirely.

If the transaction happens on the same website, as the test, you don't need to do anything. The user has a cookie that attributes the version of the test to the revenue tracking in your testing software (Optimizely, VWO). Once you connect the Google Analytics with testing software, you should be OK to go. If this is not the case, then you need to setup two email subscriber lists, one for each version of the test. Then manually tag email links in the emails to attribute the ecommerce revenue directly to the version of the test.

Make sure you've setup advanced analytics. You'll get a better picture of which conversions were direct, and which ones were assisted by another channel. Use tags and make sure your urls include all the detailed parameters - note that savvy users might truncate that link, so use a link shortener (like bit.ly) to mask it.

Yes. While Experiments reporting is session based, a user is kept into the test, seeing the same variation the whole time, so when they convert, they will be attributed to the test variation they have been seeing. This is limited to the same browser on the same device, so if the user changes devices (20% of the time for average eCommerce sites by my estimation) or clears cookies (1%) or changes browsers on the the same device (?), than Experiments (and nothing else legal) can track them. Hope this helps. PS(I suggest you look at other tools, as Experiments is the last tool I would recommend right now).

Do you have any interest in maintaining the domain? Is it getting regular traffic? To maintain that, you'll want to get some relevant content on the domain as quickly as possible. From there, you can decide what you want to do with it. If you just bought it for nostalgia or because it belonged to your competitor, and have no intention of doing something it with, you can do a redirect as the Google rank really won't benefit you. Let me know, -Shaun