How to produce multiple DC voltages for a single project
First you want to take a regulated 24V supply. To that you want to add a switch-mode ("Buck") regulator to drop you down to 5V.  You don't want to try using an LDO for this unless you are happy to have a heat sink the size of a small car. A good cheap choice is a "UBEC" that can take 24V in and give 5V out (I use these).

That 5V can then be fed direct into the Arduino.

Depending on what the "LED bank" is you may get away with an 18V (or adjustable) LDO, or an adjustable buck regulator. Or a simple (though high wattage) resistor may be all that is needed. You will have to provide more detail on this to get more help.