RME manufactures the best devices you can get for your money, the FF400 is no exception.
The only thing that you should question yourself is, whether you want to invest into a firewire based recording interface in 2021. Microsoft doesn't officially support Firewire anymore in Windows 10 since longer time.
There are still Firewire drivers available for Win10 and it might still work now, but nobody can tell you how long this will continue to work. From RME you only get the Firewire driver for the FF400. The Firewire driver is an older one from Microsoft and nobody knows how long the Microsoft kernel will support this old driver.
RME offers driver for Microsoft and apple and they work great, RME is known for driver quality.
You can take any DAW you like.
X10SRi-F, E5-1650v4, Win10Pro20H2, Cub11Pro, UFX+ (v0.9735), XTC, 12Mic, ADI-2 Pro FS R BE