Starter questions about router bits

From a tools point of view it is best to have as many flutes as possible and a diameter as big as possible, because then each flute has less "cutting-stress" and more material behind the cutting edge to withstand this stress. Tools would last much longer. RPM as low as possible.

BUT

Now comes the material point of view. RPM, progress, number of flutes, flute geometry, is cooling needed ... this needs to be adjusted according to the characteristics of the material. Each material has a optimum speed for the cutting edge (meaning turning speed and not the movement of the portal), where you get a clean cut and best tool life. And you have to take care with materials that can melt.
Materials producing small chips which easily get out of the cutting path come along with many flutes.
Melting material -> less flutes.
...

AND

there are the needs of the resulting working piece. If you have corners or curves with little diameter you might want to use small diameters. If you have small details you need small diameters.
Of course a tool change costs time, so it might be better to use a tool which is as big as possible and as small as needed.
If time with a small cutter would increase too much, it might be better to mill 2 more than one step. First a rough cut, then another cut for all the details.

AND

the machine also adds some complexity. The more rigid a machine is, the more aggressive you can be with the cutting parameters.

Of course you can buy lot's of endmills for all possible situations, but you can also choose "many purpose" endmills, which will do the job - they only don't do the job as good as the perfect endmill.
The endmills I use most are the 2 flute 2mm. It is OK for Aluminum, Wood, POM, Acrylic, Polystyrol, Copper (with some tricks), PE.

Diamond endmills are best for GFK/CFK compound materials and should not be replaced with a normal cutter.

Downcut is best for flat material, because it does not pull up the material, but you have to take care about the chips not to be pushed beneath the material.

Best is to watch out for threads where the parameters are listed and start with those. Even if alluminum is not alluminum and wood is not wood and POM is not POM ... 😆

A lot of useful info here, thanks a lot!