If your bike is going to live outside, I would clean and wax everything you can.
There has been some debate over WD-40 and its lubricating properties, I think in your case, keeping your sprockets coated with WD-40 will help repell, and displace some of the water. Also, use a good chain lube, I used to get a spray from Honda, Blue Stuff or something like that, that won't fling off when you are riding.
I also use a chrome polish from Mothers - available at walmart. It will help prevent corrosion on your exhaust system.
I have heard that a good bike cover will allow air circulation around the bike, while also shielding against water. I think a tarp would trap moisture, causing more problems.
I guess that is all the best advice I can offer. I have had my bike in the rain a few times, and can't find any sign of rust or corrosion, but it is kept in a garage.