Synths to complement existing ones:
Personally I would hesitate to get either of these today. Those encoders are hard to replace and are starting to fail at this point in time. My personal favorite wavetable/wavesequencing synth is the Korg Wavestation, and they are really cheap right now. Get an EX or AD version.
Moog Sub 37
Weird combo for ambient. I haven't heard the Sub 37 yet but I wasn't that impressed with the Sub Phatty which was what it is based on. Xpander is a classic but again make sure the encoders are all working well and that the displays are functioning, they don't make those displays anymore. And skip the Japanese version, when I worked at Oberheim we had lots of trouble with them.
Yamaha 01v96i digital mixer/audio interface/daw control
Yamaha has made some nice digital boards, this is one of their low end ones and is getting a bit long in the tooth. It will work but their are better options out there that do the same thing. Take a look at the presonus studio/live boards.
Neumann KH 120
Neumann doesn't make monitors, those are Klein + Hummel monitors re-branded when Sennheiser bought them out. On the positive side they are still highly regarded monitors. I've never used them but they get very good reviews.
Beyerdynamic DT-770 Pro 32 Ohm
Their was another thread here recently about headphones, you might want to take a look at that one to see what others have said.
Eventide Eclipse or Valhalla Plugins
Lots of choices here, I don't have any Eventide stuff but I do like them. Valhalla a lot of people love but I've never used them. I already have tons of hardware reverb choices. Yeah I know, not much help here.
Is this your only microphone? And what do you plan to record with it? The SM57 has two things going for it, it's cheap and its built like a tank. They sound ok, not great. I would not get this as my one studio mic. If I had to use it in the studio recording you could get away using it on a snare drum or maybe a nasty Fender Twinreverb amp. The only other thing I would use it for is a live concert setting on something not critically important. If you want a cheap mic for the studio that sounds decent I'd go with a Rhode NT2 or something similar. If you have the money an AKG 414 is a pretty good all around mic with multiple patterns.
Sennheiser MKH 416-P48U3
We have one of those Roland recorders at work and the internal mics in that thing suck. And the Sennheiser, do you really need a super-cardioid mic for something specific? If you are interested in doing field recording I wouldn't get this, the field is too narrow in my opinion. Daw:
Cubase AI (free license with yamaha 01v96i) or Protools
Free Cubase, well you get what you pay for.
And I don't like Protools, I'm more of a Logic fan, but you have to be mac based then.
There, is that helpful?