Macaroni is good in the fridge for up to 5 days.
If you want to keep the macaroni longer than 5 days you should place the macaroni in a sealed container and freeze it.
When frozen the macaroni will keep in the freezer for up to a year although it's at best quality for 3 to 6 months after freezing it.
The best and easiest way to keep macaroni from absorbing mayonnaise is to allow the macaroni to cool down and chill the macaroni first after cooking it.
After cooking the macaroni you should chill the macaroni in the fridge for 20 minutes or until cool enough and then add the mayonnaise to the macaroni.
The chilled macaroni will not absorb the mayonnaise like warm or hot macaroni would.
Or at least allow the macaroni to cool off some before adding the mayonnaise to the macaroni and then it should not absorb the mayonnaise as much.
Also tossing the macaroni with some oil such as olive oil can also help prevent the absorbing of the mayonnaise.
Pasta absorbs liquids, because it is made of starch, and starch absorbs water.
Tossing the pasta or macaroni with oil will reduce the absorption of the mayonnaise, by coating them in a water-repellent layer.
Also don't drain as much water from the cooked pasta, and add more dressing.
There's a limit to how much moisture pasta will absorb.