To be honest, I can't tell all that much difference between the keyboards of my YPT-400, PSR-E433, PSR-E443, and PSR-EW400. Minor differences, perhaps, but they all feel fine to me. However, I'm not much of a player-- my skills are kind of minimal, and I play almost entirely with just my right hand, so I don't play two-handed piano music on my keyboards.
Maybe if I did, I'd have more of an opinion about how the keys feel, but to me the different models feel equally okay for playing monophonic synth style.
With regard to DAWs, I suggest you try out some free trials-- or free lite versions if available-- to get an idea of what's out there and see which one does what you need and in the way you want. I happen to like Acoustica Mixcraft for creating splits and layers, and playing virtual instruments, because I think it's really easy to use for that. But Mixcraft doesn't handle SysEx-- and neither do Ableton Live and PreSonus Studio One, by the way-- although you can download a set of free plug-ins from Cockos that can be used for SysEx. Steinberg Cubase is a good all-around professional DAW that does handle SysEx, but you need to buy a dongle to use it-- unless you get the most basic version, which doesn't require a dongle. There are many others out there, so my advice is to take your time deciding which one you want to spend your money on, and in the meantime give the free trials a spin.