You will need pure argon gas (or Ar/He mix for thick metal.)
For 4043 wire you would need to use 0.9mm wire. 0.8mm will not feed reliably without a spool gun. Expect to use a wire and gun speed over twice what you are used to with steel.
With 5356 wire, you can use almost any size as it is stiffer. Wire and gun speed are just a bit faster.
The choice of wire depends on the application. There are many different Al alloys.
5656 has problems of boundary cracking when used with some alloys and it runs at elevated temperatures (>150F). Some say they have never seen the problem. There seem to be specific combinations of base/wire alloys that have the failure. Most just say don't use 5356 on something that will live at elevated temps. So a manifold would not be a good idea to use 5356. It is easy to feed and is stronger than 4xxx wires.
4043 is soft and melts a at lower temperature, so not a lot of penetration and wire feed speed needs to be high. Also, many smaller MIGs can not lower the voltage. Birdnesting is a problem with 0.8mm wire. I found 0.9mm works well.
AL is 3 to 5 times as conductive as steel. So in shirt circuit mode, it will draw high pulse currents. Should be no problem with a portamig. You can blow out diodes on low-end MIGs using Al wire.