Want to drain/change compressor oil, but there’s no outlet

You don't really need an "air compressor" in the sense that you don't need something that has a tank and is designed for use with tools. All you really need is sometimes called a "tire inflator", obviously it is actually an air compressor but it is very different from those listed by Jeff's answer.

I have seen two basic types.

There are 12V versions that are designed to simply plug into the cigarette lighter outlet in your car. This is nice because you can refill the tires anywhere. When I had a slow leak in my tire I put this thing in the trunk and drove to work, then before leaving work I would top off the tire again. It worked fine for the day or two until I could get to the shop for a new tire. Usually these are pretty cheap.

The other version is designed to plug into a household receptacle. These seem to be a little more expensive than the 12V versions.

Sometimes you can find these types of tire inflators with standalone battery jumpers attached so you can also use it to jump your car. I would skip that feature unless you think you would actually use it.

First off, I'm no expert on compressor/air type sprayers. Most of the time, these type sprayers are used for very thin paints such as automotive, lacquers etc. They also have fairly small paint reservoirs attached to the gun itself. They tend to put out a lot of over spray and should be used in a controlled area like a spray booth with proper ventilation. I never see this type of sprayer on building jobs.

The airless sprayer, such as the one you noted, use a high pressure pump to push paint through the hose to the gun. They deliver a good pattern (depending on tip selected), are easily controlled and since they don't mix air with the product, have far less atomazation of paint in the air. the other huge advantage is that the pick-up hose can be put directly into your 1 or 5 gallon can of paint. Follow the directions on priming and cleaning, but it is easy. I personally have a Graco model 17 and love it. It is a professional grade sprayer and retails around $450-$500. Just two weeks ago, I and a helper painted and back-rolled a complete two story house and detached garage in one day.(very long day, however!) This saved 3 or 4 extra days of labor and the results were fantastic. We shot both semi-trans stain on the house and matching color solid stain on the garage. This sprayer handled both products easily. (I always use apx 10 to 15% flowtrol with thicker solid latex based products)

The only disadvantage of this type of sprayer is on very small jobs. It takes about a pint or more of paint to fill a 25 foot hose and closer to 1/2 gallon for a 50 ft hose when priming the unit. This amount product is usually wasted at the end of the job when you get ready to clean the pump.

From the type of jobs you plan to do, I would recommend the airless sprayer hands down.